Differentiate between RocksDB error and no result

[holtgrewe]

Is your feature request related to a problem? Please describe.
We currently cannot differentiate between RocksDB query errors and empty results because of limitations in annonars.

Describe the solution you'd like
Properly handle errors and allow returning empty results in annonars CLI modules, so we can build on this change in the worker.

Describe alternatives you've considered
N/A

Additional context

• https://github.com/bihealth/varfish-server-worker/blob/5f782aee705ba360b2b0e6e94761d43f99bb99f6/src/seqvars/query/annonars.rs#L111-L115
• https://github.com/bihealth/varfish-server-worker/blob/5f782aee705ba360b2b0e6e94761d43f99bb99f6/src/seqvars/query/annonars.rs#L144-L149
• https://github.com/bihealth/varfish-server-worker/blob/5f782aee705ba360b2b0e6e94761d43f99bb99f6/src/seqvars/query/interpreter/clinvar.rs#L40-L43
• https://github.com/bihealth/varfish-server-worker/blob/5f782aee705ba360b2b0e6e94761d43f99bb99f6/src/seqvars/query/output/variant_related.rs#L62-L70
• https://github.com/bihealth/varfish-server-worker/blob/5f782aee705ba360b2b0e6e94761d43f99bb99f6/src/seqvars/query/output/variant_related.rs#L94-L103

[holtgrewe]

Prerequisite done in varfish-org/annonars#256.

Will be solved as part of #201.