Add a configuration for an index cache ttl

[SungJin1212]

Add a configuration for an index cache ttl. The index cache ttl can be configured by -blocks-storage.bucket-store.index-cache.redis.index-ttl and -blocks-storage.bucket-store.index-cache.memcached.index-ttl

Which issue(s) this PR fixes: Fixes #

Checklist

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

[SungJin1212]

@yeya24 I agree with your thoughts. Different TTLs are necessary to consider block range. There is a necessary to set of different TTL based on block meta's MaxTime and MinTime. But, the cache interface is dependent on the thanos. I think if the TTL parameter is added to StorePostings, StoreExpandedPostings, and StoreSeries funcs, the implementation is possible. c.f. https://github.com/thanos-io/thanos/blob/main/pkg/store/cache/cache.go#L43

[yeya24]

@SungJin1212 Agree. I think it would be useful to extend the interface to support TTL. The TTL could be a function that takes block metadata info as a parameter so that we know we use longer TTL for L4 blocks.

[SungJin1212]

@yeya24 Yes. If then, more optimization can be done.

[CharlieTLe]

Hello @SungJin1212, thank you for opening this PR.

There is a release in progress. As such, please rebase your CHANGELOG entry on top of the master branch and move the CHANGELOG entry to the top under ## master / unreleased.

Thanks, Charlie

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