Improve insert codegen for autogenerated columns

[sake92]

When inserting an autogenerated column, we should usually skip it.

E.g. in H2 they have GENERATED ALWAYS AS IDENTITY, in this case we should always skip it, or else it throws an error.

There is also GENERATED BY DEFAULT AS IDENTITY, which is a bit harder.
Here we can add id: Option[PK] = None and use it only if not None.