feat(dev-infra): support for caretaker note label in merge script (#37595) (#37778)

Adds support for a caretaker note label to the merge script.
Whenever a configured label is applied, the merge script will
not merge automatically, but instead prompt first in order
to ensure that the caretaker paid attention to the manual
caretaker note on the PR. This helps if a PR needs special
attention.

PR Close #37595

PR Close #37778

dev-infra/pr/merge/messages.ts

@@ -0,0 +1,15 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import {red} from '../../utils/console';
+
+import {PullRequest} from './pull-request';
+
+export function getCaretakerNotePromptMessage(pullRequest: PullRequest): string {
+  return red('Pull request has a caretaker note applied. Please make sure you read it.') +
+      `\nQuick link to PR: ${pullRequest.url}`;
+}