expand value set command should allow for configurable materialized values

Current the tool assumes you want to refer to a materialized enum PV by its curie; in fact this may vary, others may want

* expanded URLs
* labels
- with or without space replacement to camelcase/uppercase etc
* ad-hoc schemes such as MIxS `combine harvester [AGRO:00000473]`
* others

We can't anticipate all forms but we can allow passing in of an fstring (I don't think this should be schema-driven), with save evaluation materializing as preferred

Start with the implementation of the expand value set command and trace how materialized enum values are currently represented by CURIEs. Define how a caller supplies an f-string and how save-time evaluation materializes the preferred value; done should support configurable CURIE, URL, label, and ad-hoc formats.

Written by the indexing model from the issue text.