Last Seen for Users

**Is your feature request related to a problem? Please describe.**
Not related to a problem, but would be a QoL feature for server admins.
Having a Last Seen for user administration would be nice to know when the user was last active. This may be useful as part of potential clean-ups, be it on MAS or on other OIDC providers which connect to MAS.

**Describe the solution you'd like**
The addition of a "Last seen" field for user administration, alongside the already existing ones.

**Describe alternatives you've considered**
Going by OIDC provider info solely, which may not be an option for anyone without a separate OIDC provider.