[frontend/users administration] Add statistics and research field

[Drumor]

Is your feature request related to a problem? Please describe. Based on our local instance, the number of users increase drastically. The paging system keeps the page usable but it still remains difficult to search a specific user. In another hand, some data (number of submissions, registered courses,...) are still missing.

Describe the solution you'd like

1. Add a research/filter field based on the existent templates (research in submissions is a good example).
2. Add extra information on users (number of submissions, registered courses,...) to avoid bad operations.

Describe alternatives you've considered There is no alternatives considered.

Additional context The cake is a lie :cake: