Add layer quality checklist to contributor docs

[MattF-NSIDC]

:warning: Please wait to merge this PR after merging #711, which includes a new document (disclaimer.md) this PR depends on. Merge main in to this branch to resolve the build failure.

Description

Closes #615

Checklist

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

• [x] Config lockfile updated (inv config.export > qgreenland/config/cfg-lock.json)
• [x] Version bumped if needed (bumpversion (major|minor|patch|prerelease|build)
• [x] CHANGELOG.md updated
• [x] Documentation updated if needed
• [x] New unit tests if needed

[MattF-NSIDC]

RTD is failing:

/home/docs/checkouts/readthedocs.org/user_builds/qgreenland/checkouts/716/doc/contributor/how-to/contribute-layers.md:115: WARNING: 'myst' reference target not found: /disclaimer.md

It will pass once #711 is merged and this branch is updated from main.