feat: add generated_file field for MergeRequestDiff

• Please check this box if this contribution uses AI-generated content (including content generated by GitLab Duo features) as outlined in the GitLab DCO & CLA. As a benefit of being a GitLab Community Contributor, you receive complimentary access to GitLab Duo.

https://docs.gitlab.com/api/merge_requests/#list-merge-request-diffs

Added the missing generated_file field to the MergeRequestDiff object as described in the documentation above.