Add possibility to restrict uid based routes

Problem/Motivation

Especially the main core route entity.user.canonical (user/{user} based on uid) gives feedback about existing users (Access denied if exist and Page not found if not). This can be automatically checked by an external script.

Steps to reproduce

check /user/{user} path

Proposed resolution

Create option to block entity.user.canonical and all the uid routes which are not needed because of u3id alternatives.

Remaining tasks

User interface changes

API changes

Data model changes