Expanded DM toggling/controls

[amity]

Purpose: To ensure that players that aren't supposed to be DMs, aren't, at the start of a session.

I'm open to ideas on the implementation, I was thinking either:

• Command that prints a list of all DMs in the channel (so they can be told to change)
• Command that makes the user a DM, and all other users in the channel/with a role non-DMs.

Potentially, we could also have an automatic function to setup the bot to post in a specific channel if a user makes themself a DM in direct message (to avoid people using DM tools on the side), but that seems a bit excessive.