Add a "test" mode for validating metadata without publishing

[WardLT]

Is your feature request related to a problem? Please describe.
I am preparing a notebook and don't want to publish now, but I won't know if I'm close to correct until we try to publish.

Describe the solution you'd like
A "dry run" function on publication that tests against the schema and ensures the data are accessible, but does not create a record in Foundry.

Describe alternatives you've considered
Publish then ask Foundry to delete my incomplete dataset.

Additional context
Add any other context or screenshots about the feature request here.

[ascourtas]

This was handled in #377 for #218 -- the user can now run f.validate_metadata()

Closing until further notice