Upgrade term and constraint bindings to structures

Various notes from SEC meeting:

local value sets could be in

• Terminology Service ( )

• In archetype - just more bindings ( )

• separate associated ‘sibling’ artefact ( )

says need local value sets in template - should act like an 'implementation guide'.

downside: numerous special templates, just to accommodate the needed rate of changes / updates.

: use FHIR value-sets approach - could they be inside a source template - e.g. from a governance / mgt point of view.

: ideally separated from templates (ref: Norway).

TB: future could be to treat source template as multiple artefacts (files) ; compile with appropriate options into OPT which does act as a standalone artefact, including any locally needed value sets.