[RFC] Option in config to have return values based on schema nullability

### What happened?

In #375 we discussed and changed the resolvers return from this:

for `query { user: User! }` we generate `func (r *Query) User(ctx context.Context) (User, error)`
for `query { user: User }` we generate `func (r *Query) User(ctx context.Context) (*User, error)`

to always this:

`query { user: User }` ---> `func (r *Query) User(ctx context.Context) (*User, error)`

### What did you expect?

To have in config something like: `omit_slice_element_pointers: false` (for slices) to have not pointer return values for resolvers.

Does it make sense or am I wrong?