World Ocean Atlas 2023 salinity layers

[trey-stafford]

Description

Add salinity layers from the World Ocean Atlas. These mirror the existing temperature layers from WOA (same depths and witner/summer seasonal averages).

Checklist

If an item on this list is done or not needed, check it with [x] or click the checkbox.

• [x] The PR description links to issues that it resolves with closes #{issue_number}
• [x] Config lockfile updated (inv config.export > qgreenland/config/cfg-lock.json)
• [x] Environment lockfile updated if needed (conda-lock)
• [x] Version bumped if needed (bumpversion (major|minor|patch|prerelease|build))
• [x] CHANGELOG.md updated (for user-facing changes)
• [x] Documentation updated if needed
• [x] New unit tests if needed

[trey-stafford]

Adds ~2.1M to the package (uncompressed).

[trey-stafford]

Resolves https://github.com/nsidc/qgreenland/issues/510.