RFE: Support custom struct tags

[ajeddeloh]

It would be good to support allowing specifying struct tags in some way. JSON schema doesn't have a concept which maps nicely to it, but maybe something like additionalProperties or comments could be hijacked for use. For Ignition I'm trying to find a way to note additional metadata about each key (specifically which one acts as a unique identifier for the struct) and struct tags would be ideal.