proxy: metrics2 (#5179)

## Problem

We need to count metrics always when a connection is open. Not only when
the transfer is 0.

We also need to count bytes usage for HTTP.

## Summary of changes

New structure for usage metrics. A `DashMap<Ids, Arc<Counters>>`.

If the arc has 1 owner (the map) then I can conclude that no connections
are open.
If the counters has "open_connections" non zero, then I can conclude a
new connection was opened in the last interval and should be reported
on.

Also, keep count of how many bytes processed for HTTP and report it
here.

libs/consumption_metrics/src/lib.rs

@@ -107,7 +107,7 @@ pub const CHUNK_SIZE: usize = 1000;
 
 // Just a wrapper around a slice of events
 // to serialize it as `{"events" : [ ] }
-#[derive(serde::Serialize)]
+#[derive(serde::Serialize, serde::Deserialize)]
 pub struct EventChunk<'a, T: Clone> {
     pub events: std::borrow::Cow<'a, [T]>,
 }