Support ActiveDirectory backend for user-info-fetcher

[sbernauer]

Background
We currently only support KeyCloak as a backend for the UserInfoFetcher. This allows pull through access to Active Directory in theory, but is an extra component to manage, that can be unneeded, when everything should come from AD anyway.

We should look into supporting Active Directory as a direct backend for the UserInfofetcher.

Implementation Tasks

• UserInfoFetcher: ActiveDirectory backend #622

[lfrancke]

Can you please link the docs for this and add a snippet for the release notes?