Config actions/labeler to label config changes

This will make it clearer when a PR touches the config, or just does
something unrelated (e.g. Node dependendency bumps).

Author: sambostock

.github/labeler.yml

@@ -0,0 +1 @@
+"config change": rubocop.yml

.github/workflows/labeler.yml

@@ -0,0 +1,15 @@
+name: "Pull Request Labeler"
+on:
+- pull_request_target
+
+jobs:
+  triage:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v4
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"
+        sync-labels: true