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.

proxy/src/proxy.rs

@@ -7,6 +7,7 @@ use crate::{
     compute::{self, PostgresConnection},
     config::{ProxyConfig, TlsConfig},
     console::{self, errors::WakeComputeError, messages::MetricsAuxInfo, Api},
+    metrics::{Ids, USAGE_METRICS},
     protocol2::WithClientIp,
     stream::{PqStream, Stream},
 };
@@ -602,6 +603,11 @@ pub async fn proxy_pass(
     compute: impl AsyncRead + AsyncWrite + Unpin,
     aux: &MetricsAuxInfo,
 ) -> anyhow::Result<()> {
+    let usage = USAGE_METRICS.register(Ids {
+        endpoint_id: aux.endpoint_id.to_string(),
+        branch_id: aux.branch_id.to_string(),
+    });
+
     let m_sent = NUM_BYTES_PROXIED_COUNTER.with_label_values(&aux.traffic_labels("tx"));
     let mut client = MeasuredStream::new(
         client,
@@ -609,6 +615,7 @@ pub async fn proxy_pass(
         |cnt| {
             // Number of bytes we sent to the client (outbound).
             m_sent.inc_by(cnt as u64);
+            usage.record_egress(cnt as u64);
         },
     );