Add predicates to WebHook for disabled states

What does this MR do and why?

This MR adds predicate methods to WebHook and its subclasses for the three disabled states that the model can encounter:

• Be permanently disabled due to recent 5xx status codes from the remote server
• Be temporarily disabled due to recent 4xx status codes from the remote server
• Be rate limited due to excessive calls

These predicate methods will be used by the frontend #345165 (closed) and allows us to refactor some backend code to use them.

MR acceptance checklist

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

Related to #345165 (closed)