Move mute to timeouts

Discord now has broad availability of the `timeouts` feature, which bypasses role hierarchy checks for muting users, as well as proper client support on all platforms, it would be interesting to migrate the muting punishment to use it, as it would not require any extra setup and will always work as long as the bot has `MODERATE_MEMBERS`.

The only downside I can think of is that timeouts are limited to 28 days iirc, but then again imo if you mute someone for longer than that just ban them.

Locate the current muting punishment implementation and any related tests, then review Discord's timeout API and the MODERATE_MEMBERS requirement. Done means muting uses timeouts instead of the existing role-based mechanism while accounting for the 28-day limitation.

Written by the indexing model from the issue text.