Resolve "API: /groups/:name query very slow for groups with many projects"

What does this MR do?

Improves the performance of /groups/:id API endpoint by adding an optional parameter to omit the group projects details.

Why was this MR needed?

The performance on /groups/:id was slow

Screenshots (if relevant)

TBA

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
• Conform by the database 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?

Closes #42415 (closed)