Use gnomAD v4 variants for annotation in ClinVar data pipeline

[nawatts]

ClinVar variants are annotated with gnomAD AC, etc. The ClinVar GRCh38 data pipeline currently uses gnomAD v3 for this.

https://github.com/broadinstitute/gnomad-browser/blob/b4e38686e23fe4a31ff7c9541fe78b82b4df286b/data-pipeline/src/data_pipeline/pipelines/clinvar_grch38.py#L56-L65