Add validation rules

[lopierra]

• ontology term prefix, e.g. MONDO/HP - ensures that label/term aren't switched, and consistency (e.g. SNOMED vs SNOMEDCT)
• Unknown - preferred over NA
• Age at X contigent on X not being unknown/blank (e.g. age only required for vital status Alive or Dead, not Unknown) [@madanucd to check whether this is possible in LinkML]
• Participant ID has to be unique within a Study

[lopierra]

@madanucd here is an example of a validation rule that is needed:

In the Participant class, if outcomesVitalStatus == "Alive" or "Dead" then ageAtLastVitalStatus is required
If outcomesVitalStatus == "Unknown" or NA then ageAtLastVitalStatus is not required

Or

If participantLifeSpanStage (Study) == Pediatric then ageAtFirstPatientEngagement (Participant) must be <0 and <=6209 days