Move cluster permissions check to dashboard service subclass

What does this MR do?

This MR moves the (lack of) permission check for the cluster dashboard service to the dashboard subclass, rather than keeping that logic in the base service.

This changes no behavior - user-facing or otherwise. Just a teeny refactor.

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

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers