Docs for Project/Groups members API with inherited members

What does this MR do?

Updates the docs: expains the differences between GET api/projects/:id/members and GET api/projects/:id/members/all related to inherited members.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #51404 (closed)