Send webhook when a merge request review is submitted

Messias Tayllanrequested to merge
gitlab-community/gitlab-org/gitlab:592358-submit-review-webhooks into master

What does this MR do and why?

Send webhook when a merge request review is submitted

Submitting a review with "Request changes" or "Reviewed" updated the reviewer state but never fired a merge request webhook, so external integrations received no event for the action. Approvals and re-request review already emit webhooks, leaving submitted reviews as the remaining gap.

MergeRequests::UpdateReviewerStateService now captures the reviewer hook attributes before the update and executes the merge request hooks with an "update" action, reusing the reviewer-state diff already built for re-request review. Only the submitted-review states fire the webhook: approve and unapprove keep their own dedicated webhooks, and the automatic review_started/unreviewed transitions stay silent to avoid duplicate or noisy events.

Changelog: added

References

How to set up and validate locally

  1. Configure a project or group webhook with Merge request events enabled.
  2. Open a merge request and assign a reviewer.
  3. As the reviewer, start a review by commenting on a diff line.
  4. Complete the review, select Request changes (or Reviewed), and submit.
  5. Confirm a merge_request webhook fires with action: "update" and a changes.reviewers entry showing the new state.
  6. Confirm that approving still fires only the approved webhook (no duplicate update event).

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