refactor(app_configuration): update feed ad settings form logic

- Replace separate frequency and placement interval fields with a single enabled toggle for each role
- Restructure ad configuration model to use a map for role-specific settings
- Update controller initialization and value updating logic to reflect new model
- Modify tab change listener to enforce business rules for premium users
- Update ad frequency and placement interval retrieval methods
- Remove unnecessary switch statements and simplify configuration updates

Author: fulleni