Create a new dataset definition of observations in a particular encounter

It would be helpful to be able to export observations for a particular encounter, such as the last or first encounter (of a certain type). Such as:

• 'The RETURN VISIT DATE from the most recent APPOINTMENT encounter', or
• 'The WEIGHT from the first ART_INITIAL encounter'

This would be a new dataset definition type, which would include the following:

• Columns: PatientId, EncounterId, encounter.encounterDatetime, ObsId, Obs.concept.name, Obs.value, obs.obsDatetime
• Only allow a single concept to be chosen, and a single encounter type
• It uses the input cohort given in the report.