Update browser for gnomAD v4.1 (checklist)

[ch-kr]

Ticket to track various v4.1 data loading / update requests

Loading requests:

• [x] #1439 | (@phildarnowsky-broad) Update code parsing SV and CNV files to accommodate updates, including updated metrics order, updated genetic ancestry terms, update from using gender to sex karyotype and reload SV, CNVs
• [x] (@rileyhgrant) Load demo with PCSK9 (see thread) to get feedback on new flags below
• [x] (@rileyhgrant) Load demo that contains only new gene constraint results (HT path shared here; gs://gnomad/v4.1/constraint/metrics/gnomad.v4.1.constraint_metrics.ht)
• [ ] #1463 | (@rileyhgrant, @nadeaujoshua) Reload short variant exome and genome data
• [ ] #1443 | (@rileyhgrant) Update downloads page links to point to new data
• [ ] (riley to merge PRs, work done by methods team -- thank you!) Apply changes to help pages; current PRs:
  • [ ] #1430 | HT help page -- Qin added a few minor edits due to the slightly tweaked joint freq HT schema
  • [x] #1433 | v4.0>v4.1 updates -- this PR has been approved and is ready to go (note that I added a minor update to the dataset selection page on Apr 4)
  • [x] #1456 | Exome capture regions
  • [x] #1465 | describe new joint freq stats
  • [ ] #1476 | Add new flags to flags help page (new PR)
• [ ] #1448 (@phildarnowsky-broad)| Make non-ukbb a selectable subset

Updates:

• [x] #1423 | (@rileyhgrant) Add new flag indicating when a variant was not called in any data type
• [x] #1442 | (@rileyhgrant) Add new flag for variants with discrepant frequencies between the exomes and genomes
• [ ] #1440 | (@rileyhgrant) Update stats page to include number of samples in the two of the v4.0 exomes subsets
• [x] #1458 | (@rileyhgrant) Not necessarily v4.1, but update typos on stats page
• [ ] (no issue) | (@rileyhgrant) Update stats page to include average number of SNVs per person (still being calculated) -- edit to add that this has been pushed to post-v4.1 (hoping to have shortly afterwards)
• [ ] (no link yet) Release v4.1 blog post when v4.1 data are loaded (methods team to stage, review, and approve staged post; will add link to PR when it exists)

Feedback

• [x] #1475 | (@rileyhgrant) ticket tracking feedback on v4.1 demo browser

Will add updates if I've missed anything and as we create links for some of the topics above!

Also including v4.1 release checklist