Add mirror pipeline for v3.x branch (#601)

* Add mirror pipeline

* Remove master

Author: castrodd

code-mirror.yml

@@ -0,0 +1,18 @@
+trigger:
+    branches:
+        include:
+            - v2.x
+            - v3.x
+
+resources:
+    repositories:
+        - repository: eng
+          type: git
+          name: engineering
+          ref: refs/tags/release
+
+variables:
+    - template: ci/variables/cfs.yml@eng
+
+extends:
+    template: ci/code-mirror.yml@eng