Support querying for variants by accession

[holtgrewe]

Is your feature request related to a problem? Please describe.
Sometime it is useful to refer to variants by their accession (e.g., dbSNP, ClinVar). We do not support this yet in reev.

Describe the solution you'd like
Recent annonars versions already have column families that allow access by accession to ClinVar and dbSNP on the CLI.

• expose dbSNP by accession
• expose ClinVar and ClinVar SV by accession in annonars server

Allow users to access variants by accession

• dbsnp rs* case insensitive
• ClinVar VCV*/RCV* case insensitive, ignoring versions

Describe alternatives you've considered
N/A

Additional context
N/A