Added with_stats option to GET /projects/:id/repository/commits (API)

What does this MR do?

It allows do display stats for a commit in /repository/commits endpoint. A parameter with_stats was introduced to that.

Are there points in the code the reviewer needs to double check?

Don't think so

Why was this MR needed?

We aggregate information about commits and usually also interested in stats to have the full picture. Before it required us to get an additional request to repository/commits/:sha/diff what very slow and sometimes we exceed limits.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• [-] Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?