feat: add helper functions for generating CSV reports

[Ang-m4]

Description

This pull request adds the logic needed to generate CSV reports for enrollments, courses, and learners.
For this, I implemented new helper functions that can read serializer data (or any dictionary) and resolve nested values using the __ notation.

Key changes

• Added a new reports helper to handle CSV report generation with some utility functions for nested field lookups.
• Added three new report endpoints:
  • /manage/catalogs/<id>/enrollments/report
  • /manage/catalogs/<id>/learners/report
  • /manage/catalogs/<id>/courses/report

How to test

1. Make sure you have a catalog with:
   • Learners assigned,
   • Courses added,
   • Enrollments created.
2. Go to the Swagger UI and locate the new report endpoints under the manager section.
3. Call:
   • /manage/catalogs/<id>/enrollments/report
   • /manage/catalogs/<id>/learners/report
   • /manage/catalogs/<id>/courses/report