[FEAT]: access to the subissues preview api

[paulpach]

Describe the need

Our org uses the subissues preview feature

I am not able to access the extra fields with octokit.graphql.net. There does not appear to be a way to pass the preview feature header or access the "parent" field.

related to #130

SDK Version

No response

API Version

No response

Relevant log output

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[github-actions]

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