Restore data migration instructions for Node.js and REST (#134)

* Restore data migration instructions for Node.js and REST

* Fix header levels

* Revamp to use directus SDK

* Fix wording issue

content/tutorials/4.migration/promoting-changes-between-environments-in-directus.md

@@ -32,3 +32,206 @@ When you need to migrate content as part of schema updates, you have several opt
    - [Custom extensions migrations](/self-hosting/including-extensions)
    - Direct database operations (being careful with system tables)
    - Using and modifying the [template CLI](https://github.com/directus-community/directus-template-cli) to extract and load of all schema, system collections and content.
+
+
+## Migrate Your Schema
+
+Directus' schema migration endpoints allow users to retrieve a project's data model and apply changes to another
+project.
+
+This is useful if you make changes to a data model in a development project and need to apply them to a production
+project, or to move from a self-hosted project to Directus Cloud.
+
+### How-To Guide
+
+::callout{icon="material-symbols:info-outline"}
+
+**Permissions**<br/>
+
+You must be an admin user to use these endpoints and follow this guide.
+
+::
+
+You should have two Directus projects - this guide will refer to them as the "base" and the "target".
+
+::tabs
+    ::div{class="pr-6"}
+    ---
+    label: Node.js
+    ---
+    #### Set Up Project
+
+    Open a new empty directory in your code editor. In your terminal, navigate to the directory and install dependencies
+    with `npm install @directus/sdk`.
+
+    Create a new `index.js` file and set it up:
+
+    ```js
+    import { createDirectus, authentication, rest, schemaSnapshot, schemaDiff, schemaApply } from '@directus/sdk';
+    const BASE_DIRECTUS_URL = 'https://your-base-project.directus.app';
+
+    const TARGET_DIRECTUS_URL = 'https://your-target-project.directus.app';
+
+    const baseDirectus = createDirectus(BASE_DIRECTUS_URL).with(rest());
+    const targetDirectus = createDirectus(TARGET_DIRECTUS_URL).with(rest());
+
+    await baseDirectus.login('base_email', 'base_password');
+    await targetDirectus.login('target_email', 'target_password');
+
+    async function main() {}
+
+    main();
+    ```
+
+    #### Retrieve Data Model Snapshot From Base Project
+
+    At the bottom of `index.js`, create a `getSnapshot()` function:
+
+    ```js
+    async function getSnapshot() {
+      return await baseDirectus.request(schemaSnapshot());
+    }
+    ```
+
+    Note that the data property is destructured from the response and returned. In the `main()` function, call
+    `getSnapshot()`:
+
+    ```js
+    async function main() {
+      const snapshot = await getSnapshot(); // [!code ++]
+      console.log(snapshot); // [!code ++]
+    }
+    ```
+
+    Get your snapshot by running `node index.js`.
+
+    #### Retrieve Data Model Diff
+
+    This section will create a "diff" that describes all differences between your base and target project's data models.
+
+    At the bottom of `index.js`, create a `getDiff()` function which accepts a `snapshot` parameter:
+
+    ```js
+    async function getDiff(snapshot) {
+      return await targetDirectus.request(schemaDiff(snapshot));
+    }
+    ```
+
+    Update your `main()` function:
+
+    ```js
+    async function main() {
+      const snapshot = await getSnapshot();
+      console.log(snapshot); // [!code --]
+      const diff = await getDiff(snapshot); // [!code ++]
+      console.log(diff); // [!code ++]
+    }
+    ```
+
+    Get your diff by running `node index.js`.
+
+    #### Apply Diff To Target Project
+
+    At the bottom of `index.js`, create a `applyDiff()` function which accepts a `diff` parameter:
+
+    ```js
+    async function applyDiff(diff) {
+      return await targetDirectus.request(schemaApply(diff));
+    }
+    ```
+
+    Update your `main()` function:
+
+    ```js
+    async function main() {
+      const snapshot = await getSnapshot();
+      const diff = await getDiff(snapshot);
+      console.log(diff); // [!code --]
+      await applyDiff(diff); // [!code ++]
+    }
+    ```
+
+    Apply the diff by running `node index.js`.
+
+    ### Handling Different Directus Versions
+
+    The diff endpoint does not allow different Directus versions and database vendors by default. This is to avoid any
+    unintentional diffs from being generated. You can opt in to bypass these checks by adding a second query parameter
+    called `force` with the value of `true`.
+
+    The hash property in the diff is based on the target instance's schema and version. It is used to safeguard against
+    changes that may happen after the current diff was generated which can potentially incur unexpected side effects when
+    applying the diffs without this safeguard. In case the schema has been changed in the meantime, the diff must be
+    regenerated.
+
+    The complete and final code is available below.
+
+    ```js
+    import { createDirectus, authentication, rest, schemaSnapshot, schemaDiff, schemaApply } from '@directus/sdk';
+    const BASE_DIRECTUS_URL = 'https://your-base-project.directus.app';
+
+    const TARGET_DIRECTUS_URL = 'https://your-target-project.directus.app';
+
+    const baseDirectus = createDirectus(BASE_DIRECTUS_URL).with(rest());
+    const targetDirectus = createDirectus(TARGET_DIRECTUS_URL).with(rest());
+
+    await baseDirectus.login('base_email', 'base_password');
+    await targetDirectus.login('target_email', 'target_password');
+
+    async function main() {
+      const snapshot = await getSnapshot();
+      const diff = await getDiff(snapshot);
+      await applyDiff(diff);
+    }
+
+    main();
+
+    async function getSnapshot() {
+      return await baseDirectus.request(schemaSnapshot());
+    }
+
+    async function getDiff(snapshot) {
+      return await targetDirectus.request(schemaDiff(snapshot));
+    }
+
+    async function applyDiff(diff) {
+      return await targetDirectus.request(schemaApply(diff));
+    }
+    ```
+    ::
+    ::div{class="pr-6"}
+    ---
+    label: REST API
+    ---
+    #### Retrieve Data Model Snapshot From Source Project
+
+    Perform a `GET` request to `/schema/snapshot?access_token=<YOUR_ACCESS_TOKEN>`.
+
+    Copy the JSON response with your data model snapshot.
+
+    #### Retrieve Data Model Diff
+
+    This section will create a "diff" that describes all differences between your source and target project's data models.
+
+    Perform a `POST` request to `/schema/snapshot?access_token=<YOUR_ACCESS_TOKEN>`, with the "Content Type" header set to `application/json` and the body set to the contents of the `data` property of JSON response from the snapshot.
+
+    Copy the JSON response with your data model diff.
+
+    #### Apply Diff To Target Project
+
+    Perform a `POST` request to `/schema/apply?access_token=<YOUR_ACCESS_TOKEN>`, with the "Content Type" header set to `application/json` and the body set to the contents of the `data` property of JSON response from the snapshot.
+
+    Note the response status of 204, which indicates a successful data model migration.
+
+    ### Final Tips
+
+    The diff endpoint does not allow different Directus versions and database vendors by default. This is to avoid any
+    unintentional diffs from being generated. You can opt in to bypass these checks by adding a second query parameter
+    called `force` with the value of `true`.
+
+    The hash property in the diff is based on the target instance's schema and version. It is used to safeguard against
+    changes that may happen after the current diff was generated which can potentially incur unexpected side effects when
+    applying the diffs without this safeguard. In case the schema has been changed in the meantime, the diff must be
+    regenerated.
+    ::
+  ::