feat(span_concentrator): replace std map with hashbrown for better performances (#1234)

feat(span_concentrator): replace std map with hashbrown for better performances

# Motivations

Creating and checking for the existence of the aggregation key is the most expensive operation performed by data-pipeline if there is a high drop rate.

Currently this operation is not optimal as equality has to go through virtual dispatch because of limitations on the std hashmap.

Changing to hashbrown gives us:
* A more efficient hashing function
* We can implement the Equivalent trait instead of the borrow trait to compare owned and borrowed key, which performs better
* We can drop the Cow and just use either String or &str
* We can use the entry API on the hashmap so we don't have to potentially access the hashmap twice

These changes bring a 25% perf improvement on the span concentrators benchmarks

# Changes

* Use hashbrown::HashMap instead of std::HashMap in the stats collector
* Replace AggregationKey<'static> with OwnedAggregationKey
* implement hashbrown::Equivalent instead of Borrow

Merge branch 'main' into paullgdc/data-pipeline/stats_collector_hmap

Author: paullegranddc

Cargo.lock

@@ -30,6 +30,7 @@ tokio = { version = "1.23", features = [
 ], default-features = false }
 uuid = { version = "1.10.0", features = ["v4"] }
 tokio-util = "0.7.11"
+hashbrown = { version = "0.15" }
 
 ddcommon = { path = "../ddcommon", default-features = false }
 ddtelemetry = { path = "../ddtelemetry", default-features = false }