Enabling PR auto-labeling (#15020)

* Create labeler.yml

Creating the initial label mappings

* Adding the auto-labeler workflow

.github/labeler.yml

@@ -0,0 +1,6 @@
+area-mvc:
+  - src/ProjectTemplates/**/*
+  - src/Razor/**/*
+
+area-blazor:
+  - src/Components/**/*

.github/workflows/labeler.yml

@@ -0,0 +1,11 @@
+name: "Pull Request Labeler"
+on:
+- pull_request
+
+jobs:
+  triage:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v2
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"