Add CLA workflow (#118)

.github/workflows/cla.yml

@@ -0,0 +1,33 @@
+name: "CLA Assistant"
+on:
+  issue_comment:
+    types: [created]
+  pull_request_target:
+    types: [opened,closed,synchronize]
+  merge_group:
+    branches:
+      - main
+
+permissions:
+  actions: write
+  contents: write
+  pull-requests: write
+  statuses: write
+
+jobs:
+  CLAAssistant:
+    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') && github.repository_owner == 'forem'
+        uses: contributor-assistant/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PERSONAL_ACCESS_TOKEN: ${{ secrets.CLA_PERSONAL_ACCESS_TOKEN }}
+        with:
+          path-to-signatures: 'signatures/version1/cla.json'
+          path-to-document: 'https://github.com/forem/forem/blob/main/CLA.md'
+          branch: 'main' # branch should not be protected
+          allowlist: ${{ secrets.CLA_ALLOWLIST }}
+          remote-repository-name: ${{ secrets.CLA_REPOSITORY }}
+          lock-pullrequest-aftermerge: false