[Actions] Add action to bump the hash used for the unified pipeline (#7712)

Context: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions
Context: https://github.com/xamarin/sdk-insertions/wiki/Unified-pipeline#github-actions

Add a GitHub Actions Workflow in
`.github/workflows/sdk-insertion-bump.yml` which is run when new
commits are made to the `main` and `release/**` branches.

The GitHub Action will get the information of the updated branch and
send that commit informtaion to the xamarin/sdk-insertions repo using
a client payload via [`repository_dispatch`][0].  The event with the
payload is the parsed by
[xamarin/sdk-insertions/.github/workflows/sdk-bump.yml][1], which
updates various YAML files for the [unified insetion pipeline][2].
This allow to have the unified pipeline build the latest commits of
the SDKs without a manual trigger.

Co-authored-by: Peter Collins <pecolli@microsoft.com>

[0]: https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#repository_dispatch
[1]: https://github.com/xamarin/sdk-insertions/blob/85976c35520b21cbde62a9412c8525ac2a5f4b84/.github/workflows/sdk-bump.yml
[2]: https://github.com/xamarin/sdk-insertions/wiki/Unified-pipeline#requirements

Author: mandel-macaque

.github/workflows/sdk-insertion-bump.yml

@@ -0,0 +1,35 @@
+name: Notify release branch change
+
+on:
+  # trigger for main and release branches.
+  push:
+    branches:
+      - main
+      - 'release/**'
+
+jobs:
+  pingRemote:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Parse commit
+        shell: pwsh
+        id: commit_title
+        run: |
+          Write-Host "Commit message is $Env:COMMIT_MESSAGE"
+          $title = ($Env:COMMIT_MESSAGE -split '\n')[0]
+          "COMMIT_TITLE=$title" >> $env:GITHUB_OUTPUT
+        env:
+          COMMIT_MESSAGE: "${{ github.event.head_commit.message }}"
+
+      - name: 'Update remote repository'
+        uses: peter-evans/repository-dispatch@v2
+        with:
+          token: ${{ secrets.SERVICEACCOUNT_PAT }}
+          event-type: 'sdk_insertion' 
+          repository: 'xamarin/sdk-insertions'
+          client-payload: '{"repository": "xamarin/xamarin-android", "branch": "${{ github.ref_name }}", "commit": "${{ github.sha }}", "commit_message": "${{ steps.commit_title.outputs.COMMIT_TITLE }}"}'
+
+