add distro build

build/azure-pipelines/distro-build.yml

+steps:
+- task: NodeTool@0
+  inputs:
+    versionSpec: "10.15.1"
+
+- script: |
+    set -e
+
+    cat << EOF > ~/.netrc
+    machine github.com
+    login vscode
+    password $(VSCODE_MIXIN_PASSWORD)
+    EOF
+
+    git config user.email "vscode@microsoft.com"
+    git config user.name "VSCode"
+
+    git remote add distro "https://github.com/$VSCODE_MIXIN_REPO.git"
+    git fetch distro
+    git merge $(node -p "require('./package.json').distro")
+
+  displayName: Merge Distro
\ No newline at end of file