[server] install custom sql scripts before creating tables for the schema
A cube might need something like 'CREATE EXTENSION postgis' before
creating tables for its entities, to add new final types.
for table, column in [
('transactions', 'tx_time'),
('tx_entity_actions', 'tx_uuid'),
('tx_relation_actions', 'tx_uuid')]:
repo.system_source.create_index(session, table, column)
commit()