Sub-issue endpoint

[wtf403]

Describe the feature or problem you’d like to solve

Enable replication of current projects workflows, enhancing issue management flexibility

Proposed solution

Add sub-issue endpoint

Additional context

https://github.blog/changelog/2025-01-13-evolving-github-issues-public-preview

https://docs.github.com/en/rest/issues/sub-issues

[wtf403]

#117

[SamMorrowDrums]

#235

[e7217]

@wtf403 @SamMorrowDrums
Hello, it seems that this issue is not progressing.
Would it be okay if I proceed with supporting the sub-issue feature?

[a-man-called-q]

@SamMorrowDrums it seems like #470 is available now.