Update Gnomad SNV version

[Jakob37]

The latest Gnomad version is now 4.0.0

We are running version 2.1 for exomes and genomes, and 3.1 for mitochondria.

Link to Gnomad download page

[Jakob37]

• [x] Start download
• [x] Complete download
• [x] Parse into the correct format
• [ ] Prepare files on Hopper to be ready for transfer
• [ ] Update the version in the pipeline