Add VC => RDF data model check for issuer instances that only use VC-JWT or JCS

[dlongley]

If an issuer instance is configured to only use VC-JWT or JCS, then an additional check should be performed that converts an incoming VC to RDF (w/safe mode enabled) to catch mistakes in the submitted data.

[dlongley]

The JCS cryptosuites are handled now, but we still need to run a check for envelopes like VC-JWT.