Add CLA github action (#91)

* Add cla workflow

* change cla link in cla github action

.github/workflows/cla.yml

@@ -0,0 +1,26 @@
+name: 'CLA Assistant'
+on:
+  issue_comment:
+    types: [created]
+  pull_request_target:
+    types: [opened, closed, synchronize]
+
+jobs:
+  CLAssistant:
+    runs-on: ubuntu-latest
+    steps:
+      - name: 'CLA Assistant'
+        if: (github.event.comment.body == 'recheckcla' || github.event.comment.body == 'I have read the CLA Document and I hereby sign the CLA') || github.event_name == 'pull_request_target'
+        # Alpha Release
+        uses: gnosis/cla-github-action@master
+        # GitHub token, automatically provided to the action
+        # (No need to define this secret in the repo settings)
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          path-to-signatures: 'signatures/version1/cla.json'
+          path-to-cla-document: 'https://gnosis-safe.io/cla/'
+          branch: 'cla-signatures'
+          allowlist: germartinez,mikheevm,rmeissner,Uxio0,dasanra,davidalbela,luarx,giacomolicari,lukasschor,tschubotz,gnosis-info,bot*
+          empty-commit-flag: false
+          blockchain-storage-flag: false