Adding the .yml file for the pipeline for mirroring the GitHub repo to Azure DevOps

.azure/pipelines/azure-pipelines-mirror.yml

@@ -1 +1,50 @@
-# This is a placeholder for Azure Mirror Github pipeline
+resources:
+  repositories:
+  - repository: GarnetGithubRepo
+    type: github
+    name: microsoft/garnet
+    endpoint: ADO_to_Github_ServiceConnection
+    trigger:
+      branches:
+        include:
+        - main
+
+pool:
+  vmImage: 'ubuntu-latest'
+
+jobs:
+- job: MirrorGithubToADO
+  displayName: 'Mirror GitHub main to Azure DevOps main'
+  pool:
+    vmImage: 'ubuntu-latest'
+  steps:
+  - checkout: GarnetGithubRepo
+    clean: true
+    persistCredentials: true
+
+  - script: |
+      # Set up Git identity  
+      git config user.email "$(GIT_USER_EMAIL)"
+      git config user.name "$(GIT_USER_NAME)"
+      git config --global credential.helper 'cache --timeout=3600'
+
+      # Fetch the latest changes from the GitHub main branch
+      git fetch origin main
+
+      # Check out main branch locally
+      # git checkout main
+
+      # Ensure the local main branch is checked out and reset to match origin/main
+      git checkout -B main origin/main
+
+      # Reset the main branch to match the origin/main branch
+      # git reset --hard origin/main
+
+      # Push the updated main branch to Azure DevOps
+      git -c http.extraheader="AUTHORIZATION: bearer $(System.AccessToken)" push https://dev.azure.com/msresearch/_git/Garnet main
+
+    displayName: 'Mirror GitHub main to Azure DevOps main'
+    env:
+      GIT_USER_EMAIL: $(GIT_USER_EMAIL)
+      GIT_USER_NAME: $(GIT_USER_NAME)
+      SYSTEM_ACCESSTOKEN: $(System.AccessToken)