feat: always set omitempty on pointer fields

[obitech]

When optional: "pointer" is configured, omitempty is needed for input fields for the generated code to be semantically correct. Without omitempty an empty pointer would generate an "empty value" which is incorrect.

Consider the following graphql schema generated by Hasura:

input task_insert_input {
  id: Int
}

Without this fix, the following golang struct will be generated:

type Task_insert_input struct {
  Id: *int `json:"id"`
}

• Ref: https://github.com/Khan/genqlient/issues/260
• Ref: https://github.com/Khan/genqlient/pull/264

I have:

• [x] Written a clear PR title and description (above)
• [x] Signed the Khan Academy CLA
• [ ] Added tests covering my changes, if applicable
• [x] Included a link to the issue fixed, if applicable
• [x] Included documentation, for new features
• [x] Added an entry to the changelog

[justonia]

What's the status on this? I'm working with the Linear API and it's broken if omitempty isn't supported.

[staugaard]

I'm also waiting for this feature.

[benjaminjkraft]

Closing in favor of #308 which uses a config option