this diff consist in 4 revisions:
- tests: use stock pytest_postgresql factory function instead of the custom factory_fact.
- mark postgresql_fact fixture factory function as deprecated
- move initialize_database_for_module in db_utils to prepare the deprecation of db/pytest_plugin.py; it's the only function from db/pytest_plugin.py still in use.
- deprecate the module entirely.
Closes T4285.