Add a pipeline for automated VMR synchronization (#14805)

Adds a pipeline that will trigger on main commits and synchronize the [VMR](https://github.com/dotnet/dotnet).
The pipeline has 2 parameters:
- What commit of installer to sync to (defaults to commit that triggered the build)
- What branch of the VMR it pushes to (defaults to branch that triggered the build)

eng/pipelines/templates/jobs/vmr-synchronization.yml

@@ -0,0 +1,76 @@
+### These steps synchronize code from product repositories into the VMR (https://github.com/dotnet/dotnet)
+
+parameters:
+- name: targetRef
+  displayName: Target revision in dotnet/installer to synchronize
+  type: string
+  default: $(Build.SourceVersion)
+
+- name: vmrBranch
+  displayName: dotnet/dotnet branch to use
+  type: string
+  default: $(Build.SourceBranchName)
+
+- name: vmrToken
+  displayName: PAT that allows pushing to dotnet/dotnet
+  type: string
+
+jobs:
+- job: Synchronize
+  displayName: Synchronize dotnet/dotnet
+  timeoutInMinutes: 120
+
+  pool:
+    ${{ if eq(variables['System.TeamProject'], 'public') }}:
+      name: NetCore-Public
+      demands:
+      - ImageOverride -equals Build.Ubuntu.2004.Amd64.Open
+    ${{ else }}:
+      name: NetCore1ESPool-Internal
+      demands:
+      - ImageOverride -equals Build.Ubuntu.2004.Amd64
+
+  steps:
+  - checkout: self
+    clean: true
+    displayName: Checkout dotnet/installer
+    fetchDepth: 0
+    path: installer
+
+  - checkout: vmr
+    clean: true
+    displayName: Checkout dotnet/dotnet
+    fetchDepth: 0
+    path: vmr
+
+  - script: |-
+      source ./eng/common/tools.sh
+      InitializeDotNetCli true
+      ./.dotnet/dotnet tool restore
+    displayName: Restore toolset
+    workingDirectory: $(Agent.BuildDirectory)/installer
+
+  # TODO (https://github.com/dotnet/arcade/issues/11386): Remove this step
+  # This step is here so that darc can find the PR commit (which might be in some fork)
+  # We need to make darc understand that it needs to look in the fork from this PR
+  - ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
+    - script: |-
+        cp -r $(Agent.BuildDirectory)/installer $(Agent.TempDirectory)/installer
+      displayName: '[PR Only] Prepare dotnet/installer clone'
+
+  - script: |-
+      $(Agent.BuildDirectory)/installer/.dotnet/dotnet darc vmr update --vmr $(Agent.BuildDirectory)/vmr --tmp $(Agent.TempDirectory) --azdev-pat $(System.AccessToken) --github-pat ${{ parameters.vmrToken }} --recursive --verbose installer:${{ parameters.targetRef }}
+    displayName: Synchronize dotnet/dotnet
+    workingDirectory: $(Agent.BuildDirectory)/installer
+
+  - ${{ if and(ne(variables['Build.Reason'], 'PullRequest'), eq(variables['System.TeamProject'], 'internal')) }}:
+    - script: |-
+        set -x
+        git config --global user.email 'dotnet-maestro[bot]@users.noreply.github.com' && git config --global user.name 'dotnet-maestro[bot]'
+        git remote add dotnet 'https://${{ parameters.vmrToken }}@github.com/dotnet/dotnet.git'
+        git fetch dotnet
+        git branch ${{ parameters.vmrBranch }}
+        git branch --set-upstream-to=dotnet/${{ parameters.vmrBranch }} ${{ parameters.vmrBranch }} || echo 'Branch ${{ parameters.vmrBranch }} not found in remote'
+        git push dotnet ${{ parameters.vmrBranch }}
+      displayName: Push changes to dotnet/dotnet
+      workingDirectory: $(Agent.BuildDirectory)/vmr