Context menu for infraction search

I think it'd be exceedingly helpful to quickly be able to view a user's infraction history as an ephemeral message in the same channel. The current system of going to another channel to view infraction history is quite clunky, especially on mobile.

This command should also send a non-ephemeral message in the mods channel when it's invoked, so other moderators have an indication that a particular user is being investigated.