ci: run make codegen validation in workflow

Fail if a PR is submitted and has not run "make codegen"

Signed-off-by: Sébastien Han <seb@redhat.com>

.github/workflows/codegen.yml

@@ -0,0 +1,20 @@
+name: Codegen
+on: [pull_request]
+
+jobs:
+  codegen:
+    runs-on: ubuntu-latest
+    steps:
+    - name: checkout
+      uses: actions/checkout@v1
+
+    - uses: actions/setup-go@v2
+      with:
+        go-version: 1.13
+
+    - name: run codegen
+      run: GOPATH=$(go env GOPATH) make codegen
+
+    - name: validate codegen
+      run: hack/validate-codegen.sh
+