feat: add topic model from dropdown in studio

[ahmed-arb]

Add Topic Model and Management for Studio Course Settings

Summary

This PR introduces a new Topic model and supporting utilities to enable course topic categorization in Studio. Course authors can now select from existing topics or create new ones when configuring course details.

Changes

Database & Models

• New Model: Added Topic model with name field to store available course topics
• Migration: Created initial migration 0001_initial.py for the Topic model
• Admin Interface: Registered Topic in Django admin with search and list display functionality
• New endpoint: Added a new endpoint to allow topic creation

Utilities

• get_topics(): Returns list of all available topic names for populating dropdown options
• update_other_course_settings(): Merges and saves topic data into course.other_course_settings via the advanced settings API
• Circular Import Prevention: Refactored imports to use apps.get_model() for lazy loading:
  • CourseEnrollment
  • CourseOverview

Technical Details

• Topics are stored in the wikimedia_general_topic table
• Uses model_utils.TimeStampedModel for automatic timestamp tracking
• Course topic selection is saved in other_course_settings field
• Some edx-platform model imports converted to lazy loading pattern to avoid initialization issues

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Related PRs:
edx-platform: wikimedia/edx-platform#581
frontend-app-authoring: edly-io/frontend-app-authoring#5

Ticket: wikimedia/edx-platform#569