dynamic field selection

[braindevices]

Problem

Currently you must define your selections ahead of time and cannot dynamically select fields. This is because it is impossible to statically type queries using a dynamic syntax.

• the SQLModel of fastapi actually support dynamic field selection https://github.com/fastapi/sqlmodel/issues/232#issuecomment-1068127576
• our raw query actually return dict instead of typed model

So I think it is pretty reasonable to enable the dynamic field selection, once user choose to use it the return value will be just like the raw queries.