Refactor WebHook rate-limiting code

What does this MR do and why?

Refactors the WebHook rate-limiting code to move the method call that increments the rate limit for a WebHook into the model, to be alongside the existing disabling methods #disable! and #backoff! which are also in the model.

There should be no functional changes.

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 #345165 (closed)