feat(discussion): Implement discussion moderation features

[mraman-2U]

This pull request introduces comprehensive support for discussion moderation, focusing on user banning and improved permissions, as well as adding audit-friendly Django admin interfaces for discussion moderation models. Key changes include enforcing discussion bans at the API level, filtering banned users from course stats, providing admin UIs for bans and exceptions, and sending escalation emails on ban actions. Additionally, permissions logic for moderation actions has been clarified and extended.

Discussion Moderation and Banning:

• Enforces discussion bans in the API: users who are banned cannot create threads or comments, and the ban status is exposed in API responses. Banned users are also excluded from course discussion user stats. (lms/djangoapps/discussion/rest_api/api.py) [1] [2] [3] [4] [5] [6]
• Adds Django admin interfaces for DiscussionBan and DiscussionBanException with read-only access for staff and full access for superusers, supporting audit and compliance needs. (lms/djangoapps/discussion/admin.py)
• Implements email notifications for ban escalation, using ACE if available or falling back to Django email, to alert support teams when a user is banned. (lms/djangoapps/discussion/rest_api/emails.py)

Permissions and Moderation Improvements:

• Refines and documents moderation permissions, ensuring that only appropriate roles (global staff, course staff/instructors, forum moderators/administrators) can perform bulk delete and ban actions. (lms/djangoapps/discussion/rest_api/permissions.py) [1] [2]

Serializer and Miscellaneous Updates:

• Updates discussion serializers to expose additional context (e.g., ban status, moderation privilege) and tweaks spam URL filtering logic for improved accuracy. (lms/djangoapps/discussion/rest_api/serializers.py) [1] [2] [3]…user bans

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