sdss-v add new loader for astra aspcap model

[havok2063]

Add support for SDSS-V astraASPCAP file. Add a new SDSS-V loader to support loading this file, with proper units, into Spectrum1D and Specviz. The goal would be to overlay the model spectrum on top of the mwmStar spectrum. Blocker for sdss/sdss_solara#10 .

@rileythai can you also take a look at this one?

[rileythai]

Do you know where on the SAS I can find one of these model spectra? I haven't been able to find one.

[havok2063]

Yeah, I'll Slack you since it's still proprietary data.