Add API endpoint to export courses as ZIP and backfill session data

[vikrantwiz02]

This pull request introduces a new API endpoint for exporting all course registration lists as Excel files packaged in a ZIP, and addresses issues with missing session and semester_type fields in the course_registration model. It also includes a data migration to backfill these fields for existing records and ensures they are set on new records.

New export feature:

• Added the export_all_courses_zip API endpoint, which allows academic admins and professors to export all courses (filtered by academic year, semester, programme, and list type) as individual Excel sheets bundled in a ZIP file. Each sheet contains detailed student lists, with improved formatting and instructor information. (FusionIIIT/applications/academic_information/api/views.py, FusionIIIT/applications/academic_information/api/urls.py) [1] [2]
• Imported the zipfile module to support the new export functionality. (FusionIIIT/applications/academic_information/api/views.py)

Data integrity improvements:

• Updated the verify_registration function to set the session and semester_type fields when creating new course_registration records, ensuring these fields are always populated going forward. (FusionIIIT/applications/academic_procedures/api/views.py)
• Added a Django migration to backfill session and semester_type for existing course_registration records that are missing these fields, deriving values based on semester_no and working_year. (FusionIIIT/applications/academic_procedures/migrations/0020_backfill_course_registration_session.py)