ci: add workflow for labeling new RFCs

.github/workflows/new-rfc.yml

@@ -0,0 +1,22 @@
+name: New RFC
+
+on:
+  pull_request:
+    types: [opened]
+
+jobs:
+  label-new-rfc:
+    if: github.event.pull_request.head.repo.fork == true && github.event.pull_request.title matches '^\[RFC \d+\].*$'
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+
+    steps:
+      - name: Label new RFC
+        env:
+          GH_TOKEN: ${{ github.token }}
+          GH_REPO: ${{ github.repository }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+        run: |
+          gh pr edit $PR_NUMBER --add-label "status: open-for-nominations"
+