Make modal dialog common for Groups tree app

What does this MR do?

This fixes a ~bug (as well as ~"technical debt") where Modal dialog use in Groups tree app was incorrect and it ended up with multiple Group modal instances for each Group item.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• Tests added for this feature/bug
• Review
  • [ ] Has been reviewed by UX
  • Has been reviewed by Frontend
  • [ ] Has been reviewed by Backend
  • [ ] Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• [ ] Internationalization required/considered

What are the relevant issue numbers?

Closes #41613 (closed)