Api shared projects

What does this MR do?

Exposes the shared projects in the group endpoint

What are the relevant issue numbers?

Builds upon !5148 (closed) and closes #18780 (closed)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together