filter to only GQ tag before extracting GQ tags per sample

The `extract_gq_scores` rule extracts GQ information from a VCF for every sample. Before we run this step, we could extract just the GQ information from the VCF. And then extract it for each sample, separately.
This will likely speed up the execution of `extract_gq_scores` and reduce the disk space needed for execution of the rule on the cloud

Locate the Snakemake definition of the extract_gq_scores rule and inspect how its VCF input and per-sample outputs are handled. Run the existing workflow or rule to establish current runtime and disk usage, then verify that GQ-only intermediate data produces the same per-sample results with reduced resource use.

Written by the indexing model from the issue text.