the nmdc-schema may contain some `Biosample` slots that belong exclusively to the submission-schema

[turbomam]

For example, rna_volume is defined in nmdc-schema and associated with Biosample. We even have some tests for it.

If it is important to capture that information in the SubmissionPortal, so that it can be passed on to user facilities, but it is never going to be saved into MongoDB, maybe it doesn't belong in nmdc-schema?

Right now, I don't think we have a way to introduce slots into submission-schema other than by extraction from nmdc-schema, but that doesn't seem like a big technical challenge.

see this example data file, which I revised in a currently-unmerged PR.