Add bucket index support to store gateway

[pracucci]

What this PR does:
Following up the PR #3614, in this PR I'm adding bucket index support to the store-gateway. The usage of the bucket index in the store-gateway is optional and disabled by default.

I haven't changed any integration test because the existing tests in integration/querier_test.go already covers it.

Which issue(s) this PR fixes:
N/A

Checklist

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

[pracucci]

I've opened a PR in Thanos thanos-io/thanos#3660 to export the fetcherMetrics to hopefully remove the duplicated code (even if may be tricky to integrate anyway due to the additional label values corruptedBucketIndex and noBucketIndex).

[ranton256]

LGTM

[lzh-lab]

Compactor block cleaner report an error when directory markers hava a block deletion mark which the block no longer exists.

component=cleaner org_id=fake msg="failed blocks cleanup and maintenance" err="marker not found"

[lzh-lab]

Compactor block cleaner report an error when directory markers hava a block deletion mark which the block no longer exists.

component=cleaner org_id=fake msg="failed blocks cleanup and maintenance" err="marker not found"

This will result in UpdateIndex always failure.

Maybe this should be a warning or just ignored.

[pracucci]

Compactor block cleaner report an error when directory markers hava a block deletion mark which the block no longer exists.

component=cleaner org_id=fake msg="failed blocks cleanup and maintenance" err="marker not found"

This will result in UpdateIndex always failure.

Maybe this should be a warning or just ignored.

Should be fixed by this change:
https://github.com/cortexproject/cortex/pull/3625/files#diff-821456401172c65d2c0cf8706a3d700bf213d73f6932cee9ef7d1d805693b097

If, once this PR is merge, it will happen again, then we can re-investigate it.

[pstibrany]

Excellent work, I don't see any flaws in it. Good job!