ci: add AutoPR workflow, relying on OPENAI_API_KEY env var

cf https://github.com/irgolic/AutoPR/blob/main/USAGE.md#setup

.github/workflows/autopr.yml

@@ -0,0 +1,37 @@
+on:
+  issues:
+    types: [labeled]
+
+permissions:
+  contents: write
+  issues: write
+  pull-requests: write
+
+jobs:
+  autopr:
+    if: ${{ contains( github.event.label.name, 'AutoPR') }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install jq
+        run: sudo apt-get install jq
+      - name: Check if label was added by a collaborator
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          is_collaborator=$(curl -s -H "Authorization: token $GITHUB_TOKEN" -H "Accept: application/vnd.github+json" \
+            "https://api.github.com/repos/${{ github.repository }}/collaborators/${{ github.event.sender.login }}" | jq -r '.message')
+          if [ "$is_collaborator" == "Not Found" ]; then
+            echo "Label not added by a collaborator. Skipping action."
+            exit 78
+          fi
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          ref: main
+          fetch-depth: 1
+      - name: AutoPR
+        uses: docker://ghcr.io/irgolic/autopr:latest
+        env:
+          OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}