Add a feature to close DM through community

Problem

Right now, users can DM eachother through a shared community, which is not always a bad thing. But since there is not a permission for community leaders to disable DMs through their community, or at least make it disabled for the community for people joining by default, there will be a lot of moderation crisis, like on Discord.

Proposed solution

I think there must be a permission for community leaders to disable DMs through their community, or at least make it disabled for the community for people joining, by default. It will save a lot of moderation crisis, a lesson from Discord should lead to such feature