ci: add Canonical CLA check (#303)

Author: skatsaounis

.github/workflows/cla-check.yml

@@ -0,0 +1,12 @@
+name: cla-check
+
+on:
+  pull_request:
+    branches: [master]
+
+jobs:
+  cla-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check if CLA signed
+        uses: canonical/has-signed-canonical-cla@v1