Add "API Docs" GitHub Action to check if docs are up to date

.github/workflows/api-docs.yaml

@@ -0,0 +1,22 @@
+name: API Docs
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  check-docs:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: '^1.13.1'
+      - name: gen-crd-api-reference-docs
+        run: make api-docs
+      - name: Check if docs are up to date
+        # This check must fail if there are diffs.
+        run: git diff --exit-code ./docs/api.md