Update vital query to implement new conventions for blood pressure:

By convention, systolic BP will be consider the "anchor" observation.
The corresponding diastolic BP and BP position will store the
observation_id of the systolic BP in their "value_as_concept_id" field.
For consistency, although redundant, the systolic BP observation will
also store its observation_id in it "value_as_concept_id" field. Thus
all three observations will be tied together by the observation_id of
the systolic BP observation.