Make Encounter.diagnosis optionnal

[elsiehoffet-94]

Description

Sophie @Peltier10 noticed that both Condition.encounter and Encounter.diagnosis are MustSupport attributes, which is redundant information, and causes issues with our current ETL (references can't be bound if ressource does not exist).

Considering that in most cases, diagnoses are declared administratively at the end of a patient's admission (for billing purposes), the diagnosis attribute will not be present systematically in the Admissions table. What do you think about keeping Condition.encounter as MustSupport, and making Encounter.diagnosis optional?