[ci] Add job to run after Xamarin.Android pipeline (dotnet#6881)

Context: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/pipeline-triggers

A new pipeline has been added to capture build information from the
Xamarin.Android pipeline, which can than be processed by our older
UI-style release definitions.

The Xamarin.Android pipeline often has known or acceptable test
failures in the builds that we want to release, and old UI-style
release definitions will not run against partially failed builds.
This new pipeline avoids that limitation as it will always be green.
The new pipeline will also publish information about the
Xamarin.Android build that triggered it, which will allow an old
UI-style release definition to download artifacts from the
Xamarin.Android build using the [DownloadPipelineArtifact][1] task.

A [pipeline resource][0] controls the automatic triggering of this
new pipeline, and it will run once the `post_build` stage in the
Xamarin.Android pipeline completes successfully.

The classic VS insertions will look like this:

 1. A `Xamarin.Android` pipeline build finishes.

 2. A new build of `Xamarin.Android Release Trigger` will run
    automatically.

 3. This pipeline publishes a file containing `Xamarin.Android` build
    and pipeline ID information.

 4. The `Xamarin.Android - VS + VSM Release Insertion` release
    definition uses the build and pipeline ID to download the SBOM
    artifact in the corresponding `Xamarin.Android` build.

This new pipeline can also be used to "transfer" other build
artifacts from the `Xamarin.Android` pipeline to other release
definitions in the future if needed.

[0]: https://docs.microsoft.com/en-us/azure/devops/pipelines/process/resources?view=azure-devops&tabs=schema#define-a-pipelines-resource
[1]: https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/utility/download-pipeline-artifact?view=azure-devops#arguments

build-tools/automation/azure-pipelines-release-trigger.yaml

@@ -0,0 +1,44 @@
+# Xamarin.Android Release Definition Trigger
+
+name: $(Build.SourceBranchName)-$(Build.SourceVersion)-$(Rev:r)
+
+trigger: none
+pr: none
+
+resources:
+  pipelines:
+  - pipeline: xamarin-android
+    source: Xamarin.Android
+    trigger:
+      stages:
+      - post_build
+
+jobs:
+- job: release_trigger
+  displayName: Upload Info from Triggering Build
+  timeoutInMinutes: 30
+  pool: VSEngSS-MicroBuild2022-1ES
+  workspace:
+    clean: all
+  steps:
+  - checkout: none
+
+  - powershell: |
+      $triggeringBuild = @{
+          "triggeringBuild" = @{
+              "id" = "$(Build.TriggeredBy.BuildId)"
+              "pipeline" = "$(Build.TriggeredBy.DefinitionId)"
+              "project" = "$(Build.TriggeredBy.ProjectID)"
+          }
+      }
+      $json = $triggeringBuild | ConvertTo-Json
+      New-Item -Path $(Build.StagingDirectory) -Name triggering-build.json -ItemType file -Value $json -Force
+      $jsonContent = Get-Content "$(Build.StagingDirectory)\triggering-build.json" | ConvertFrom-Json
+      Write-Host Triggering Build Info: $jsonContent.triggeringBuild.project - $jsonContent.triggeringBuild.pipeline - $jsonContent.triggeringBuild.id
+    displayName: write triggering-build.json
+
+  - task: PublishPipelineArtifact@1
+    displayName: upload triggering-build-info
+    inputs:
+      artifactName: triggering-build-info
+      targetPath: $(Build.StagingDirectory)\triggering-build.json