Add Task Model to Track Mentee Progress on GitHub Issues

[arkid15r]

Describe the solution you'd like

We want to enhance our mentorship platform by introducing a new Task model to track mentees' progress on issues they’re working on. This will serve as a bridge between GitHub issues and our internal mentorship structure (Programs, Modules, Mentees).

Goals:

• Track GitHub issues assigned to mentees
• Automatically link all issues w/ a specific label to a Module
• Associate each task with a specific Module
• Enable deadline and status tracking
• Allow arbitrary metadata storage (e.g. estimated points)
• Build UI to assign and view tasks per mentee and module

Some high-level structure:

• module: FK to Module
• issue: FK to Issue
• assignee: FK to Mentee
• assigned_at: DateTimeField
• deadline_at: Optional DateTimeField
• metadata: JSONField (optional)

The Module models needs to be updated w/ optional labels field that will be used for automatic issues linking.
The task will be created manually by mentors based on available issues when a contributor indicates their interest to start working on it.