Restrict creation of personal repositories

Currently there is no way to stop users from creating repositories on their own personal space.

Users can either go to their personal space and create a repository by using the "Create Repository" button or they can also fork a repository in a Project that they have "read" permission into their own personal space.

A reported use case asks for the following:

• Ability to restrict repository creation in an attempt to avoid users creating repositories that the "admin" does not have control over.

• A better way as a "admin" to find all personal repos (this was already reported on STASH-3564) and allow the "admin" to clean them up.

• Use case seems to be concerned on how to clean off personal repositories or eventual "garbage" that was left to lower disk usage down if necessary.