New page to explain context methods and variables available in proper…

…ties YAML files (#5840)

[Preview](https://docs-getdbt-com-git-dbeatty-properties-yml-context-dbt-labs.vercel.app/reference/dbt-jinja-functions/dbt-properties-yml-context)

## What are you changing in this pull request and why?

We have pages that describe the available rendering context for these:
-
[`dbt_project.yml`](https://docs.getdbt.com/reference/dbt-jinja-functions/dbt-project-yml-context)
-
[`profiles.yml`](https://docs.getdbt.com/reference/dbt-jinja-functions/profiles-yml-context)
-
[`on-run-end`](https://docs.getdbt.com/reference/dbt-jinja-functions/on-run-end-context)

But not for these:
- [`packages.yml` and/or
`dependencies.yml`](https://docs.getdbt.com/docs/build/packages#use-cases)
- [properties YAML
files](https://docs.getdbt.com/reference/configs-and-properties)(e.g.,
`properties.yml`, `schema.yml`, `_models.yml`, `_unit_tests.yml`,
`whatever_name_you_want.yml`, etc.)

This PR addresses the rendering context for **properties YAML files**.
`packages.yml` and `dependencies.yml` will need to be covered in a
separate PR.

## Checklist
- [x] Review the [Content style
guide](https://github.com/dbt-labs/docs.getdbt.com/blob/current/contributing/content-style-guide.md)
so my content adheres to these guidelines.

Adding pages:
- [x] Add page in `website/sidebars.js` (wasn't needed)
- [x] Provide a unique filename for new pages

---------

Co-authored-by: Mirna Wong <[email protected]>

website/docs/reference/dbt-jinja-functions/properties-yml-context.md

@@ -0,0 +1,34 @@
+---
+title: " About properties.yml context"
+sidebar_label: "properties.yml context"
+id: "dbt-properties-yml-context"
+description: "The context methods and variables available when configuring resources in a properties.yml file."
+---
+
+The following context methods and variables are available when configuring
+resources in a `properties.yml` file.
+
+**Available context methods:**
+- [env_var](/reference/dbt-jinja-functions/env_var)
+- [var](/reference/dbt-jinja-functions/var)
+
+**Available context variables:**
+- [target](/reference/dbt-jinja-functions/target)
+- [builtins](/reference/dbt-jinja-functions/builtins)
+- [dbt_version](/reference/dbt-jinja-functions/dbt_version)
+
+### Example configuration
+
+<File name='properties.yml'>
+
+```yml
+# Configure this model to be materialized as a view
+# in development and a table in production/CI contexts
+
+models:
+  - name: dim_customers
+    config:
+      materialized: "{{ 'view' if target.name == 'dev' else 'table' }}"
+```
+
+</File>