fix: noisy broker subscription failed error during storage broker d…

…eploys (#10521)

During broker deploys, pageservers log this noisy WARN en masse.

I can trivially reproduce the WARN message in neon_local by SIGKILLing
broker during e.g. `pgbench -i`.

I don't understand why tonic is not detecting the error as
`Code::Unavailable`.

Until we find time to understand that / fix upstream, this PR adds the
error message to the existing list of known error messages that get
demoted to INFO level.

Refs:
-  refs #9562

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

@@ -164,9 +164,10 @@ pub(super) async fn connection_manager_loop_step(
                     Ok(Some(broker_update)) => connection_manager_state.register_timeline_update(broker_update),
                     Err(status) => {
                         match status.code() {
-                            Code::Unknown if status.message().contains("stream closed because of a broken pipe") || status.message().contains("connection reset") => {
+                            Code::Unknown if status.message().contains("stream closed because of a broken pipe") || status.message().contains("connection reset") || status.message().contains("error reading a body from connection") => {
                                 // tonic's error handling doesn't provide a clear code for disconnections: we get
                                 // "h2 protocol error: error reading a body from connection: stream closed because of a broken pipe"
+                                // => https://github.com/neondatabase/neon/issues/9562
                                 info!("broker disconnected: {status}");
                             },
                             _ => {