Introduce a new Diagnosis domain object, backed by a new `encounter_diagnosis` table

class Diagnosis extends BaseOpenmrsData {
  Encounter encounter; // required
  CodedOrFreeText diagnosis; // required
  ConditionVerificationStatus certainty; // required
  Integer rank; // required. must be a positive integer, and it's okay for two diagnoses in an encounter to have the same rank. (As compared to previous EMRAPI implementation, 1=PRIMARY, 2=SECONDARY)
  Condition condition; // optional. May refer to a new condition to be created as a result of this diagnosis, or an existing condition that this encounter is following up.
}

class Encounter {
    // ...
   Set<Diagnosis> diagnoses 
}