Make it possible to redefine the userprofile schema

The UserProfile object is a great way to extend a user profile in the application.

As a document object, it comes with very useful features like permission which makes it easy to make properties editable by the user himself.

However the userprofile schema is restricted in studio. Instead of simply forbidding, allowing modifications with a warning that the schema is used in the application would allow for more configuration flexibility.

Reproduction steps:
In studio, try to create a userprofile / userprofile schema
==>
Invalid name for a schema: 'userprofile' (this name is reserved)
Invalid name for a prefix: 'userprofile' (this name is reserved)