Enhance the ExternalAnswerValueSetResolver to take a search string

[jingtang10]

Is your feature request related to a problem? Please describe.
The ExternalAnswerValueSetResolver takes a URI of the value set and resolves that to a list of codings. The implementation is provided by client application (it can load it from disk, retrieve it from a terminology server, or from hardcoded values) and this is done ONLY ONCE when the question is rendered.

However, in reality, often the valueset is too large. So a more smart version of this operation is needed if we want to integrate with a terminology server. For example, the user might type "dia" and we want to send "dia" as well as the valueset URL to the terminology server and retrieve a smaller subset of codes in the valueset to make the user experience better.

Describe the solution you'd like
We could either create a new interface, or a new API in ExternalAnswerValueSetResolver that takes not only the url but also a search string.

We should also provide a default implementation that client application can use to connect to any terminology server.

Describe alternatives you've considered
NA

Additional context
@fredhersch @dilys-l @johngrimes

Would you like to work on the issue?
@dilys-l ?

[dilys-l]

I'm happy to work on this.