debt: get the generated typescript types for the graphql schema to align with reality

[shrouxm]

Currently, optional fields in the graphql schema get translated to T | null | undefined, when as far as i know from the backend's perspective there's no difference between the two when sending data. So we should make sure that's the case, and then consolidate on a single choice of T | null or T | undefined in our graphql schema generation config.

Additional context

Hopefully, the only config change this requires is flipping this flag, but I'm not sure if that will create any migrations down the line or if that'll actually bring things into alignment with the backend.