Prometheus has had the support for handling overlapping blocks (both during compaction and querying) for a very long time, and it has been used by Thanos, Cortex, Mimir at large scale.

I propose we enable them by default now and not hard fail on finding overlapping blocks. I also propose we still have the switch to disable compaction of overlapping blocks because it is useful and required by downstream consumers with out-of-order feature (what that I mean Mimir, but will also be required by Cortex when they support out-of-order ingestion).

cc @bwplotka