querier: Remove exact chunk duplicates on StoreAPI level, potentially merging frames together.

[bwplotka]

This needs some benchmarks as well. Found in #2528

Duplicates are handled ok in terms of data correctness but it's not very efficient. In @SuperQ repro data we found 3x chunk duplications. This is when you have duplicated StoreAPI as well as sidecar + store GW overlap. (: We can totally trim this on proxy level instead of concating all.

AC:

• proxy.go returns chunks without duplications
• frames are also "compacted" on up to 1MB (or defined size).

[bwplotka]

proxy.go returns chunks without duplications was done: #2603

The defined size AC was not done and it was actually part of another ticket as well plus the idea was abandoned.