Customization of admin panel

[florimondmanca]

Is your feature request related to a problem? Please describe.
As discussed in #34 (comment), once we get base models/permissions/etc, we'll want to allow users to customize their API key admin panel as well.

Describe the solution you'd like
Document how to customize the admin (most likely via a Wiki page).

Describe alternatives you've considered

• Create a BaseAPIKeyModelAdmin: at first sight, there may not be a need for this, but this should be confirmed first.

Additional context
admin.py