vPrev->vCurrent nmdc:Database migration script on each release if needed

[dwinston]

given that a principal use case of our schema-as-software (the importable nmdc_schema package) is to support the maintenance of schema-conformant databases (e.g. nmdc:Database JSON), it seems reasonable for each schema-as-software release to include migration code from the previous release if appropriate.

@turbomam what do you think?

This even seems like something that could be supported at the linkml level...