Add the equivalent of SDK.loadTDF for NanoTDF

[ttschampel]

Getting a NanoTDF's policy object would help enable certain workflows. This behavior already exists for TDF, but not NanoTDF.

TDF SDK supports: loadTDF() returning a TDFReader where policy can be retrieved

For example get TDF data attribute policy:
sdk.loadTDF.readPolicyObject().body.dataAttributes