test: clear schema and rerun migrations instead of just dropping tables

I've created routines for dropping/recreating the public schema entirely and then rerunning all migrations. This should get us to the same state as when we've just installed/started kotahi for the first time, with all tables/functions/triggers/foreign constraints etc, plus whatever data the migrations supply, such as admin and groupManager teams and group-wide chat channels.

I have not yet modified the dumps to account for the fact that we now have a lot of the schema already in place. The dumps will need to be stripped down substantially.