We want to ensure that for a given community, role names are unique (so we don't have several instances of one role with a different set of permissions). The key is a composite key between `thread` and `name` because we don't want to prevent the same role name from occurring across several different communities (i.e. 'Moderator' should be allowed in two different communities, but cannot exist twice in
the same community).
This is the `keyserver` validation of preventing this error, the next step will involve adding some kind of client-side notice when they click 'Create' that it is a duplicate role name.
Note: Given that the ability to create custom roles has begun in this stack, there shouldn't be an instance where there is a malformed DB state (except mine) with role names besides `Admins` and `Members`, so I don't see any issues coming out of this migration.
Part of [[ https://linear.app/comm/issue/ENG-4178/support-loadingerror-states-when-creating-a-role | ENG-4178 ]].
Depends on D8431