Automate nightly Turbopack release tagging (vercel#3594)

This adds a new workflow which automatically releases nightly versions
of turbopack. Coupled with vercel/next.js#45506,
we'll be able to fully automate our release process into Next.js.

1. The process kicks of with cron every midnight-ish PST.
2. We find the latest commit that passes CI
3. We bump the latest tag version (more on this in a bit)
4. We generate a new GH release with this version

The automated tagging version will break with our current
`turbopack-YYMMDD.XYZ` release process just a bit. The tag action that
I'm using can't generate a date-like tag, it can only handle semver
(with optional prefix). So I've set it up to generate
`turbopack-MAJOR.MINOR.PATCH-nightly.XYZ` tags. The `turbopack-` here
differentiates us from Turborepo, and the `nightly` tag denotes this a
non-release software.

I hope that I've configured this correctly to always bump patches, but
I'm not 100% confident until it runs.

Fixes WEB-502

.github/workflows/turbopack-nightly-release.yml

@@ -0,0 +1,42 @@
+name: Turobpack Nightly Release
+
+on:
+  schedule:
+    - cron: "15 8 * * *" # Run every day at 00:15 PST
+  workflow_dispatch:
+
+jobs:
+  turbopack_nightly:
+    name: Cut nightly Turbopack release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout latest commit that passes CI
+        uses: talentpair/last-green-commit-action@d95cfa8
+        id: green_commit
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Tag nightly
+        id: tag_version
+        uses: mathieudutour/[email protected]
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          commit_sha: ${{ steps.green_commit.outputs.result }}
+          tag_prefix: "turbopack-"
+          # Override the default conventional commit messages
+          # so that we always generate patch releases.
+          # This would be easier if we could filter Turbopack
+          # commits from Turborepo, but that'd require a custom
+          # action.
+          custom_release_rules: ""
+          # Ensure we generate prerelease versions, not stables.
+          release_branches: ""
+          pre_release_branches: "main"
+          append_to_pre_release_tag: "nightly"
+
+      - name: Create GitHub release
+        uses: ncipollo/release-action@v1
+        with:
+          tag: ${{ steps.tag_version.outputs.new_tag }}
+          name: Turbopack Release ${{ steps.tag_version.outputs.new_tag }}
+          omitBody: true