ci: add signature assistant

Author: cwillisf

.github/workflows/signature-assistant.yml

@@ -0,0 +1,37 @@
+name: "Signature Assistant"
+on:
+  issue_comment:
+    types: [created]
+  pull_request_target:
+    types: [opened, closed, synchronize]
+
+permissions:
+  actions: write
+  contents: read
+  pull-requests: write
+  statuses: write
+
+jobs:
+  CLA-Assistant:
+    if: github.event_name == 'pull_request_target' ||
+      (
+        github.event.comment.body == 'recheck' ||
+        github.event.comment.body == 'I have read the CLA Document and I hereby sign the CLA'
+      )
+    runs-on: ubuntu-latest
+    steps:
+      - uses: scratchfoundation/scratch-agreements/.github/actions/cla-allowlist@main
+        id: cla-allowlist
+      - name: "CLA Assistant"
+        uses: contributor-assistant/github-action@ca4a40a7d1004f18d9960b404b97e5f30a505a08 # v2.6.1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # the below token should have repo scope and must be manually added by you in the repository's secrets
+          PERSONAL_ACCESS_TOKEN: ${{ secrets.GHA_AGREEMENTS_PAT }}
+        with:
+          remote-organization-name: "scratchfoundation"
+          remote-repository-name: "scratch-agreements"
+          path-to-signatures: "signatures/version1/cla.json"
+          path-to-document: "https://github.com/scratchfoundation/scratch-agreements/blob/main/CLA.md"
+          branch: "main"
+          allowlist: ${{ steps.cla-allowlist.outputs.allowlist }}