Add GraphQL mutation for merge request request changes

Gregory Havengarequested to merge
ghavenga-graphql-merge-request-request-changes into master

What does this MR do and why?

Adds a new GraphQL mutation mergeRequestRequestChanges that allows reviewers to request changes on a merge request programmatically.

Previously, requesting changes was only available via the /request_changes slash command, which required creating a note. This mutation provides a more explicit and direct API for requesting changes.

Usage 

mutation {
  mergeRequestRequestChanges(input: {
    projectPath: "gitlab-org/gitlab"
    iid: "12345"
  }) {
    mergeRequest {
      id
      title
    }
    errors
  }
}

Implementation details

The mutation uses the existing MergeRequests::UpdateReviewerStateService which handles:

  • Updating reviewer state to requested_changes
  • Creating a system note for the change
  • Removing any existing approval from the user
  • Triggering appropriate GraphQL subscriptions

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related issues

Closes: N/A (Feature improvement)

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