SpectralCoordConverter does not serialize all parameters

[nden]

The missing parameters are radial_velocity, doppler_convention, dopler_rest, redshift.

[braingram]

Those are also missing from the associated schema:
https://github.com/asdf-format/asdf-coordinates-schemas/blob/b04d5ee1f2971545fab2a1f7a75314f9a8d48682/resources/schemas/spectralcoord-1.1.0.yaml