Add rubocop rule to group routing

What does this MR do?

Adds a rubocop rule that checks if group routing resource is under scope '-'

Follow-up on #37466 (closed). Related to #29130 (closed) and !20460 (merged)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content