pageserver: include node id when subscribing to SK (#10432)

## Problem

All pageserver have the same application name which makes it hard to
distinguish them.

## Summary of changes

Include the node id in the application name sent to the safekeeper. This
should gives us
more visibility in logs. There's a few metrics that will increase in
cardinality by `pageserver_count`,
but that's fine.

pageserver/src/tenant/timeline/walreceiver/walreceiver_connection.rs

@@ -140,7 +140,7 @@ pub(super) async fn handle_walreceiver_connection(
 
     let (replication_client, connection) = {
         let mut config = wal_source_connconf.to_tokio_postgres_config();
-        config.application_name("pageserver");
+        config.application_name(format!("pageserver-{}", node.0).as_str());
         config.replication_mode(tokio_postgres::config::ReplicationMode::Physical);
         match time::timeout(connect_timeout, config.connect(postgres::NoTls)).await {
             Ok(client_and_conn) => client_and_conn?,

test_runner/regress/test_tenants.py

@@ -194,7 +194,7 @@ def test_metrics_normal_work(neon_env_builder: NeonEnvBuilder):
         io_metrics = query_all_safekeepers(
             "safekeeper_pg_io_bytes_total",
             {
-                "app_name": "pageserver",
+                "app_name": f"pageserver-{env.pageserver.id}",
                 "client_az": "test_ps_az",
                 "dir": io_direction,
                 "same_az": "false",