Wishlist: Terminology Service support

[goelalex]

This is a wishlist item

Ability to pull down and validate terminology from an external service like VSAC (vsac.nlm.nih.gov/) or something else and check that the codes that have been received are valid. Similar to the FHIR validation use case: #389 (I recognize it should be covered already). E.g. receiving a resource and checking that the LOINC, SNOMED, or RXnorm code is valid from the sender.

Even better would be the ability to embed a standard code in a newly created resource e.g. a doctor is creating a medication and we can add an RXNorm code to it immediately.

[reshmakh]

Terminology reference

[codyebberson]

Implementation discussion: #1411