proxy refactor large files (#6153)

## Problem

The `src/proxy.rs` file is far too large

## Summary of changes

Creates 3 new files:
```
src/metrics.rs
src/proxy/retry.rs
src/proxy/connect_compute.rs
```

proxy/src/serverless/conn_pool.rs

@@ -24,13 +24,12 @@ use tokio_postgres::{AsyncMessage, ReadyForQueryStatus};
 use crate::{
     auth::{self, backend::ComputeUserInfo, check_peer_addr_is_in_list},
     console,
-    proxy::{neon_options, LatencyTimer, NUM_DB_CONNECTIONS_GAUGE},
+    metrics::{LatencyTimer, NUM_DB_CONNECTIONS_GAUGE},
+    proxy::{connect_compute::ConnectMechanism, neon_options},
     usage_metrics::{Ids, MetricCounter, USAGE_METRICS},
 };
 use crate::{compute, config};
 
-use crate::proxy::ConnectMechanism;
-
 use tracing::{error, warn, Span};
 use tracing::{info, info_span, Instrument};
 
@@ -444,7 +443,7 @@ async fn connect_to_compute(
         .await?
         .context("missing cache entry from wake_compute")?;
 
-    crate::proxy::connect_to_compute(
+    crate::proxy::connect_compute::connect_to_compute(
         &TokioMechanism {
             conn_id,
             conn_info,

proxy/src/serverless/sql_over_http.rs

@@ -29,7 +29,7 @@ use utils::http::error::ApiError;
 use utils::http::json::json_response;
 
 use crate::config::HttpConfig;
-use crate::proxy::NUM_CONNECTION_REQUESTS_GAUGE;
+use crate::metrics::NUM_CONNECTION_REQUESTS_GAUGE;
 
 use super::conn_pool::ConnInfo;
 use super::conn_pool::GlobalConnPool;