Migrate to SQLAlchemy 2.x

[callebtc]

See #497

Migration guide: https://docs.sqlalchemy.org/en/20/changelog/migration_20.html

[trbouma]

@callebtc thanks for the link. I will try if I can make sense of this and actually do a PR. The biggest advantage is to get rid of the sqlalchemy_aio library which no longer seems to be maintained and is forcing older dependencies.