chore: add commitlint workflow (#9409)

* chore: add commitlint workflow

* chore: exit 1 on fail

* chore: use builtin helpurl

commitlint.config.mjs

@@ -0,0 +1,39 @@
+/**
+ * @license
+ * Copyright 2018 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Rules configuration for commitlint.
+ * https://commitlint.js.org/reference/rules.html#subject-full-stop
+ *
+ * Extends the conventional-commit spec at
+ * https://github.com/conventional-changelog/commitlint/tree/master/@commitlint/config-conventional
+ */
+
+export default {
+  extends: ['@commitlint/config-conventional'],
+  rules: {
+    // Warn if not in this list. Allow for judicious creativity.
+    'type-enum': [
+      1,
+      'always',
+      [
+        'build',
+        'chore',
+        'ci',
+        'docs',
+        'feat',
+        'fix',
+        'refactor',
+        'release',
+        'revert',
+        'test',
+      ],
+    ],
+    'subject-case': [0],
+  },
+  helpUrl:
+    'https://developers.google.com/blockly/guides/contribute/get-started/commits',
+};