Split Matrix room creation to bare minimum function and function to update all of the details
Split Matrix room creation to one bare minimum function and one function to update all of the details.
When we change the way a room is created, we currently don't have a way to migrate/update/sync the rest of the existing rooms with this same change.
If we make the split as described above, we can use the same update function during these migration phases. The migration could be a background job, one-off, whatever.