Expose user details for user in Client UI

[jacobwod]

When ActiveDirectory is used to filter maps/layers, the Backend already has information about the currently authenticated user. That information (which currently always comes from AD) is a standardised object containing some user details.

This information will come in handy in the Client UI, opening up lot of new possibilities. This issue will not provide anything very useful, other than a nice-looking avatar button that gives the user an illusion of some personalisation (see screenshot below). The goal of this issue is however to provide the underlying mechanism for sending authenticated user's data to the Client UI.

Please note that this information would only be sent to the user that is authenticated, there is no cross-sending of different users' details between accounts. Each user will only see info about himself. Still, to eliminate any privacy related concerns, this behaviour will be controllable on a per-instance-basis (via setting in .env).