[WIP] Close session after operation

[lchen-2101]

make sure to close the db session when the session is manually created, and not coming from the request object (we automatically set a db_session in the request object which does a finally: close() at end of the generator

The garbage collector is trying to clean up non-checked-in connection <AdaptedConnection <asyncpg.connection.Connection object at 0x11b4dda90>>, which will be terminated.  Please ensure that SQLAlchemy pooled connections are returned to the pool explicitly, either by calling ``close()`` or by using appropriate context managers to manage their lifecycle.
sys:1: SAWarning: The garbage collector is trying to clean up non-checked-in connection <AdaptedConnection <asyncpg.connection.Connection object at 0x11b4dda90>>, which will be terminated.  Please ensure that SQLAlchemy pooled connections are returned to the pool explicitly, either by calling ``close()`` or by using appropriate context managers to manage their lifecycle.