Allow specifying hint to sqlstorage, to only load specific fields

[kagesenshi]

Currently we default to selecting all fields in sqlstorage, which can cause bad performance. SQLAlchemy have a way to give hint to only load some fields:

https://docs.sqlalchemy.org/en/13/orm/loading_columns.html#sqlalchemy.orm.load_only

Look into providing hint at request environment to only only load some fields

[kagesenshi]

There's also deferred loading option the orm , which I'm not sure how it behaves with our current architecture

https://docs.sqlalchemy.org/en/13/orm/loading_columns.html#deferred-column-loading