CI: Add a workflow to automatically label pull requests

The labeler language is quite restrictive right now so labels are added
quite conservatively, meaning that many PRs won't get labels when it's
"obvious" they should. It will still save some manual work on those
that it can label.

.github/workflows/label.yml

@@ -0,0 +1,26 @@
+# Copyright (C) Daniel Fandrich, <dan@coneharvesters.com>, et al.
+#
+# SPDX-License-Identifier: curl
+
+# This workflow will triage pull requests and apply a label based on the
+# paths that are modified in the pull request.
+#
+# To use this workflow, you will need to set up a .github/labeler.yml
+# file with configuration.  For more information, see:
+# https://github.com/actions/labeler
+
+name: Labeler
+on: [pull_request]
+
+jobs:
+  label:
+
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
+
+    steps:
+    - uses: actions/labeler@v4
+      with:
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"