Cache Expended Posting on ingesters

[alanprot]

What this PR does:
ThisPR introduce caching expanded postings, similar to the approach used in SG, as seen in this change.

• Key Updates:
  1. Compacted Block Caching:
     • Expanded postings are cached to all queries for compacted blocks. This is safe as compacted blocks are immutable.
  2. Head Block Caching:
     • Caching is applied only to select queries containing an equal matcher for the metric name (name).
       For such cases, a seed is added to the cache key, allowing invalidation whenever a new series is added or removed for a given metric name.
     • Example:
       • Suppose the seed for cpu_utilization is 21. Queries would generate cache keys as follows:
         • sum(cpu_utilization{service="A"}) => Key: 21|head|__name__=cpu_utilization|service=A
         • sum(cpu_utilization{service="A", op="GET"}) => Key: 21|head|__name__=cpu_utilization|service=A|op=GET
  3. Head Cache Invalidation:
     On data ingestion, if a new series is added with cpu_utilization as the metric name, the seed changes, invalidating all cached entries for that metric.
  4. Memory Bound for Seeds:
     To control memory usage, a fixed-size seed slice is used. Metric names are hashed to determine their respective seed.

In load testing, this change demonstrated significant CPU and latency improvements on ingesters experiencing heavy query loads from rulers. In such cases, the same queries are evaluated constantly (every evaluation interval), and the postings are expanded for every iteration, leading to unnecessarily high CPU usage.

This are some graphs:

Flame Graphs Before and After (we can see that the after the CPU is being used mostly for the Push method, where before was mostly being used by the QueryStream method:

The idea was inspired on thanos-io/thanos#6420 and the promise based cache implementation by grafana/mimir-prometheus#14

Which issue(s) this PR fixes:
Fixes #

Checklist

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

[justinjung04]

I love the test results! Thanks for doing this!!