github: add sponsor label workflow

.github/workflows/add-labels.yml

@@ -0,0 +1,23 @@
+# A GitHub Action that labels issues/PRs if the creator is a sponsor of the owner
+# Documentation: https://github.com/JasonEtco/is-sponsor-label-action
+
+name: add labels
+
+on:
+  pull_request:
+    types: [opened]
+  issues:
+    types: [opened]
+
+jobs:
+  build:
+    name: is-sponsor-label
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: JasonEtco/is-sponsor-label-action@v1
+        with:
+          label: sponsor 💖
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}