Add a "to_specutils" method

[weaverba137]

A "to_specutils" method would convert results returned by the SPARCL client into specutils.Spectrum1D objects. Some draft requirements:

• Depending on the wavelength axis associated with each result, the results could be placed into a single Spectrum1D object, a SpectrumCollection or a SpectrumList.
• Should be able to operate on a full set of results or an individual item from a set of results.

I already have some working code in a notebook that does this conversion, it's just a matter of making it available in the client.

[weaverba137]

@jacquesalice, I found some code that appears to already do this in type_conversion.py. Is this a released feature? If so is it illustrated in any example notebooks?

[jacquesalice]

@weaverba137 it was something that Steve and I were working on a few years ago, but in late 2022 we decided to remove it from the client. According to Steve's comment in this ticket: "If it resurfaces, it will be in redesigned form." So no, it's not a released feature or shown in any of the example notebooks. This ticket kinda describes what we were trying to do at that time: https://noirlab.atlassian.net/browse/DLS-97