Extend CohortAlleleFrequencyStudyResult to categorical variation (and maybe non-Allele VRS variation)

[mbrush]

Originally posted by @Mrinal-Thomas-Epic in #234 (comment):

Currently, the focus of CohortAlleleFrequencyStudyResult is limited to Allele (or IRI reference to Allele). Additionally, "Allele" is in the class and property name (focusAllele).

However, it seems likely that one would want to also track the frequency of CNVs and SVs, most likely as a categorical variation (since its rare to have the exact same CNV or SV). It seems like gnomAD already has frequency data for these types of variants (example).

[mbrush]

Responses from original post:

From mbrush (with thumbs up from mrinal-thomas-epic):

Does gnomad ever measure frequency of non-Allele variations? If so, it makes sense to expand the range of the focusAllele attribute (and simultaneously consider changing the name of the attribute, and perhaps the profile, to be consistent with this change . . . e.g. focusVariant).

[larrybabb]

@mbrush I added a couple sentences to respond to @Mrinal-Thomas-Epic in the original discussion, please feel free to use, edit or remove after you've processed this.

[mbrush]

At present, gnomad data covers only things that the VRS spec considers Alleles. When a concrete need / real data that requires expanding the scope of the focus of the CAF Study Results, we will drive the issue forward at that time.