ci: add signature assistant workflow

Author: cwillisf

.github/workflows/signature-assistant.yml

@@ -0,0 +1,31 @@
+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:
+    runs-on: ubuntu-latest
+    steps:
+      - name: "CLA Assistant"
+        if: (github.event.comment.body == 'recheck' || github.event.comment.body == 'I have read the CLA Document and I hereby sign the CLA') || github.event_name == 'pull_request_target'
+        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: semantic-release-bot,*[bot]