Rudder

We want to make a better user experience around user management un Rudder. That most likely means putting user in some DB, evolutions to user rights, etc.

The first step is to output most of the logic into a plugin. That will helps iterate more indenpendently than the normal Rudder release cycle on the subject.

Ideally, we would have:

- a minimalistic user identification/authentication management in rudder without the plugin (file based, as today). Authentication could be augmented with the authentication plugin. Authorization would not be configurable here (only admin role), which would allow to make bigger change under the hood in the plugin.
- the plugin would bring an UI for user management.

This ticket is just the first step to allow rudder to re-read user information and so on on the plugin.