make it possible to define a Nexus Repository instance repository administration role

Expected

It should be possible to create a role that can be assigned to a user such that the user is only allowed to perform repository administration tasks. Repository admin tasks are limited to the following areas in the UI:

• Repositories
• Content Selectors
• Routing Rules
• Blob stores
• Cleanup Policies

Essentially all items listed under the Administration -> Repository section of the UI.

This must be possible without granting the user any other roles or privileges that would include other product areas. For example assigning the user 'nx-all' is currently too broad an admin scope.