Add `alert_status` and `disabled_until` to REST API hooks response

What does this MR do and why?

Adds metadata for webhooks describing the alert status.

Specifically, two new fields are added to the REST API responses for webhooks:

• alert_status: never null, one of [executable, disabled, temporarily_disabled]
• disabled_until: if alert_status === 'temporarily_disabled', a valid future timestamp.

How to set up and validate locally

Create some web hooks, and manipulate them to be enabled/disabled etc.

Then inspect the API responses.

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 #362662 (closed)