Set default values for optional field in input types

[rnovacek]

For given input

input X {
  field: str
  otherField: str
}

It changes:

• field: Optional[str] to field: Optional[str] = None if there is no pydantic field
• other_field: Optional[str] = Field(alias="otherField") to other_field: Optional[str] = Field(alias="otherField", default=None) otherwise

Resolves #74

[jhnnsrs]

Hey thanks a lot for that PR!
In general it looks good to me.

I just wonder if there is a potential issue, as unset values and nullable
values are not by default the same according to the spec:

https://spec.graphql.org/October2021/#sel-EAFdRDBBACDAl1T

Also there is a related issue on best practices in pydantic:

pydantic/pydantic#990 (comment)

However I also feel that this is maybe an edge case and this approach looks
like a good default for me. Would just maybe appreciate a bit more input on this:
@rnovacek @nocnokneo

#74 (comment)

Happy to merge this after a short deliberation though :)
Thanks a lot!

[rnovacek]

I have to admit I'm no expert in GraphQL nor Pydantic. I cannot tell if this is the correct solution. It just scratches my own itch - no need to specify all fields in an input when they are not mandatory.

[jhnnsrs]

The more i get my head around I feel like its a good compromise given the differences between pydantic and graphql and the "standard" dev experience and what people would try to achieve.
So for me it looks good. Will merge :) Thanks a lot!