Investigate the incorrect usage of .add() and .set() in M2M relationships

[Sepehr-Sobhani]

Describe the task

Our codebase contains instances where the .add() and .set() methods for handling M2M relationships have been used incorrectly. The .add() method is intended to append new relationships without affecting existing ones, while the .set() method replaces the entire set of relationships, removing any not included in the new list. Misusing these methods can lead to unintended data loss and inconsistencies in the relationships. We need to review the code for proper usage and refactor any incorrect implementations to ensure data integrity and maintainability.

Most instances of using .set() seem to involve assigning regulated_products or activities to an operation or reporting_operation.

• create_or_update_operation
• set_registration_purpose
• save_report_operation

Acceptance Criteria

• Ensure proper usage of .set() across the codebase and add regression tests if necessary.