Add API infrastructure for issue types, sub-issues, and issue
relationships (blocked-by/blocking):
- New types: IssueType, LinkedIssue, SubIssues, SubIssuesSummary,
LinkedIssueConnection
- New Issue struct fields for all Issues 2.0 data
- GraphQL query builder cases for new fields
- ExportData cases for JSON output
- Mutation functions: UpdateIssueIssueType, AddSubIssue,
RemoveSubIssue, AddBlockedBy, RemoveBlockedBy
- Helper functions: RepoIssueTypes, IssueNodeID
- Feature detection: IssueRelationshipsSupported for GHES 3.19+
(issue types and sub-issues are GA on GHES 3.17+, no detection needed)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
c00257386e