Integrate seqvars inhouse RocksDB in varfish-worker call.

[holtgrewe]

Is your feature request related to a problem? Please describe.
After #2068, we have computed an inhouse database for seqvars. However, we don't use it yet in the worker call.

Describe the solution you'd like
Use the inhouse seqvars database in the worker if present. Depends on varfish-org/varfish-server-worker#232 and #2068.

Describe alternatives you've considered
N/A

Additional context

• Create Celery task for recomputation of seqvar inhouse data. #2068
• Use in-house frequencies in "seqvars query" varfish-server-worker#232