Add alert and badge for rate-limited webhooks

What does this MR do and why?

When a webhook is rate limited, we want to show a "Disabled" badge on the index page and an alert with more information on the edit page. This allows users to know why a webhook is not working as expected.

Follows the designs in #331407[Scenario_3.png].

Changelog: added

Screenshots or screen recordings

Page	Screenshot
Webhooks index
Webhook edit

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #343993 (closed)