[TODO] Support for public entities

### Description  
Extend the access control mechanisms in the backend to add support for public entities

### Priority  
- [ ] High  
- [ ] Medium  
- [X] Low  

### Environment  
- **Component:** Backend

### Steps to Complete  
1. ~Define db field and update serializers~
2. Update the get_accessible_entities function in django
3. Update the SQL for accessible_notes function
