Update to ORM 2.0 style from ORM 1.x style

[kvchitrapu]

Current db queries use query() method from legacy 1.x ORM API. To keep in sync with SQLAlchemy, we should start moving towards SQLAlchemy 2.0 style code which uses select() for the same purpose:

https://docs.sqlalchemy.org/en/20/orm/queryguide/api.html