Introducing sub-issues: Enhancing issue management on GitHub

Introduced a new hierarchical structure for tasks within GitHub Issues, termed 'sub-issues'. This involved creating a dedicated `sub_issues` table in MySQL to store parent-child relationships and a `sub_issue_list` table to aggregate completion status for performant progress roll-up. Sub-issues are exposed via GraphQL endpoints and built using React, leveraging existing and new list-view components. The design prioritizes intuitive controls and accessibility, incorporating feedback on metadata display (issue number, repository name) in the sub-issue list.