Add a user warning system to Mjolnir

[Linerly]

Is your feature request related to a problem? Please describe. Not being able to give a warning to a user on Matrix, just like on Discord where you can use bots to give a warning to someone

Describe the solution you'd like Have Mjolnir to give a warning to a Matrix user, just like how it works with moderation bots on Discord

Describe alternatives you've considered Manually give a warning to a Matrix user

Additional context For example: using Dyno to warn a user: ?warn <user> <reason> ...and then it will send the warning to the user in a DM and log the warning as well

It can also be configured to automatically take action on a user once it has reached the maximum amount of warnings, like automatically mute the user (~~though I think it's not really possible yet in Matrix~~ just noticed that Element has an option to mute a user, and simply sets their power level below the minimum power level required to send a message), kicking, or (temporarily) banning the user for example