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/config.ts

@@ -53,6 +53,8 @@ export interface MergeConfig {
   claSignedLabel: string|RegExp;
   /** Pattern that matches labels which imply a merge ready pull request. */
   mergeReadyLabel: string|RegExp;
+  /** Label that is applied when special attention from the caretaker is required. */
+  caretakerNoteLabel?: string|RegExp;
   /** Label which can be applied to fixup commit messages in the merge script. */
   commitMessageFixupLabel: string|RegExp;
   /**