[Feature] Differentiate prometheus metric for large vs non-large notifications

Description

It would be great if there was a prometheus metric which captures the count of large notifications. We have a counter for all notifications, it would be great if either there was a separate counter for large notifications or a field which differentiates large vs small in the global counter.

Are you aware of any blockers that must be resolved before implementing this feature? If so, which? Link to any relevant GitHub issues.

Nope

Some information to help us out

• Tick this box if you plan on implementing this feature yourself.
• I have searched the issue tracker to make sure this issue is not a duplicate.

store/postgres/src/notification_listener.rs のリンク先の 394-396 行にある既存の通知カウンターから始めます。そのエントリポイントで通知サイズがどのように利用可能かを追跡し、issue で要求されているメトリクス表現を選択します。Prometheus が大きい通知と大きくない通知を区別するカウントを公開すれば完了です。