Add webhook notifications for merge request re-request review

What does this MR do and why?

Add webhook notifications for merge request re-request review

This change enhances webhook payloads for merge requests to properly track reviewer state changes when a reviewer is re-requested. It adds the 're_requested' attribute to reviewer data in webhook payloads and refactors the reviewer hook data generation code for better maintainability.

The 're_requested' attribute is always included in reviewer hook data:

• Set to true for the specific reviewer being re-requested
• Set to false for all other reviewers
• Ensures webhook consumers can identify which reviewer was re-requested

Changelog: added

References

Resolves: #420126 (closed) Supports: #517909 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Setup project with webhook following this guide: https://docs.gitlab.com/development/webhooks/#qaing-changes.
2. Add a reviewer to any merge request
3. Notice the webhook payload when the reviewer is added now includes state
4. Use the reviewer to complete a review and submit the review
5. Re-request a review from that reviewer
6. Notice the webhook payload now contains changes to the reviewer state and that a re_requested: true in the payload

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