Add additional metadata to relationships to limit to appropriate persons

Currently, all relationships are between Person and Person, with no way to limit this down to certain types of Person. However, in the "real world", you may want certain relationships to apply to only certain types of Person.

My suggestion is to add additional field(s) to the Relationship object to support this. These would allow at least the following:

• Limited to Roles. This would be particularly useful for Provider/Patient relationships, where you could say, for example, that Nurses, Doctors, or Community Health Worker relationships supported only persons that have the "Nurse", "Doctor", or "CHW" roles respectively, for example.

• Limited to Patients. Same as the above - you want to enforce that the Person on the other side of a Provider/Patient relationship is actually a Patient, rather than just a Person.