feat(ring): Add the option of having a lower consistency level

[mbarbon]

This set of changes adds an optional consistency level for ring.Ring (defaulting to existing behavior of a quorum of RF/2+1).

This setting is going to be used by a follow-up change in Mimir (draft here) to optionally use a lower consistency level in read operations to trade lower consistency for higher availability.

Checklist

• Tests updated
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

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[pracucci]

Hi! 👋 We recently merged #947 which changed the CI configuration for unit tests. To get CI passing on this PR, please rebase on the latest main branch:

git fetch origin main
git rebase origin/main
git push --force-with-lease

Thanks!