CM-26: addressing issues and improving user experience

[olewandowski1]

CM-26

CORE PR REQUIRED

Changes:

1. Prevent system errors when performing actions on benefit plans after the deletion of another plan.
2. Enhance the tooltip for the "Save" button.
3. Implement date validation to disallow setting "Date from" as a later date than "Date to" and vice versa.
4. Remove the "json_ext" field and its dependencies.
5. Fix the "canSave" function to prevent saving the form if mandatory fields are not filled.
6. Restrict saving the form if any changes were made.