feat: Modmail

[laquasicinque]

We're currently using a third party tool for modmail, there's some issues people have with needed to discord auth with it as it's on multiple servers. If we fold this into our own bot this no longer becomes a requirement. Modmail channels should also be threads so they don't get lost and can be searched.

Also add in ability to easily report messages and users from a context menu would be possible. Also automate certain common actions mods take (purposely vague)