Support pointers as the analoge to optional types in gel #383
Description
We currently do not allow using pointers in struct fields. Instead when a field is optional we have custom types. This design was intended to reduce the risk of nil pointer dereference bugs.
However a limitation of this design is that golang doesn't allow circular references in struct definitions. So if a gel schema has a circular reference it can not be modeled cleanly in golang.
Allowing pointer struct fields will remove this mismatch.