chore: adding cla check workflow

As all users making contributions into Ockam repositories needs to sign
the CLA beforehand this workflow will give prompt them for approval and
manage the persistence.

.github/workflows/cla.yml

@@ -0,0 +1,25 @@
+name: "CLA Check"
+on:
+  issues:
+    types: [opened]
+  issue_comment:
+    types: [created]
+  pull_request:
+    types: [opened, closed, synchronize]
+
+jobs:
+  cla-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: "CLA Check"
+        uses: ockam-network/cla-action@master
+        env: 
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PERSISTANCE_GITHUB_TOKEN: ${{ secrets.PERSISTANCE_GITHUB_TOKEN }}
+        with: 
+          path-to-signatures: 'cla-signers.json'
+          path-to-cla-document: 'https://www.ockam.io/learn/guides/contributions/cla'
+          branch: 'master'
+          persistance-repository: 'contributors'
+          empty-commit-flag: false
+          blockchain-storage-flag: false