[datasets] update pan-UKB datasets and make available via GCS

[pwc2]

Currently, the Hail datasets API only has the pan-UKB datasets available via the Amazon S3 bucket. This PR makes the pan-UKB datasets available via GCS as well (from the gs://ukb-diverse-pops-public bucket), and updates the summary statistics and meta-analysis MatrixTables to reflect the most up-to-date release.