infra: Create workflow which manages GitHub labels

GitHub labels will be managed by the .github/labels.yml file.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>

.github/workflows/manage-labels.yml

@@ -0,0 +1,21 @@
+name: Manage Labels
+
+on: push
+
+jobs:
+  labeler:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Run Labeler
+        if: success()
+        uses: crazy-max/ghaction-github-labeler@v2
+        with:
+          yaml_file: .github/labels.yml
+          skip_delete: true
+          dry_run: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}