litep2p: Improve metric reasons for RequestResponse errors (#5077)

This PR improves the metrics reported by litep2p on request-response
errors.

Discovered while investigating:
- #4985


We are experiencing many requests that are `Refused` by litep2p in
comparison with libp2p.
The metric roughly approximates the sum of other reasons from libp2p.
This PR aims to provide more insights.

```
{__name__="substrate_sub_libp2p_requests_out_failure_total", chain="ksmcc3", instance="localhost:9615", job="substrate_node", protocol="/b0a8d493285c2df73290dfb7e61f870f17b41801197a149ca93654499ea3dafe/sync/2", reason="Remote has closed the substream before answering, thereby signaling that it considers the request as valid, but refused to answer it."}

    Last *: 3365
    Min: 3363
    Max: 3365
    Mean: 3365
    
    
{__name__="substrate_sub_libp2p_requests_out_failure_total", chain="ksmcc3", instance="localhost:9615", job="substrate_node", protocol="/b0a8d493285c2df73290dfb7e61f870f17b41801197a149ca93654499ea3dafe/beefy/justifications/1", reason="Remote has closed the substream before answering, thereby signaling that it considers the request as valid, but refused to answer it."}

    Last *: 3461
    Min: 3461
    Max: 3461
    Mean: 3461
```

Part of:
- #4681

cc @paritytech/networking

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

substrate/client/network/src/litep2p/shim/request_response/mod.rs

@@ -24,7 +24,7 @@ use crate::{
 	peer_store::PeerStoreProvider,
 	request_responses::{IncomingRequest, OutgoingResponse},
 	service::{metrics::Metrics, traits::RequestResponseConfig as RequestResponseConfigT},
-	IfDisconnected, ProtocolName, RequestFailure,
+	IfDisconnected, OutboundFailure, ProtocolName, RequestFailure,
 };
 
 use futures::{channel::oneshot, future::BoxFuture, stream::FuturesUnordered, StreamExt};
@@ -369,10 +369,12 @@ impl RequestResponseProtocol {
 			return
 		};
 
-		let error = match error {
-			RequestResponseError::NotConnected => Some(RequestFailure::NotConnected),
-			RequestResponseError::Rejected | RequestResponseError::Timeout =>
-				Some(RequestFailure::Refused),
+		let status = match error {
+			RequestResponseError::NotConnected =>
+				Some((RequestFailure::NotConnected, "not-connected")),
+			RequestResponseError::Rejected => Some((RequestFailure::Refused, "rejected")),
+			RequestResponseError::Timeout =>
+				Some((RequestFailure::Network(OutboundFailure::Timeout), "timeout")),
 			RequestResponseError::Canceled => {
 				log::debug!(
 					target: LOG_TARGET,
@@ -387,7 +389,7 @@ impl RequestResponseProtocol {
 					"{}: tried to send too large request to {peer:?} ({request_id:?})",
 					self.protocol,
 				);
-				Some(RequestFailure::Refused)
+				Some((RequestFailure::Refused, "payload-too-large"))
 			},
 			RequestResponseError::UnsupportedProtocol => match fallback_request {
 				Some((request, protocol)) => match self.request_tx.get(&protocol) {
@@ -426,15 +428,15 @@ impl RequestResponseProtocol {
 							peer,
 						);
 
-						Some(RequestFailure::Refused)
+						Some((RequestFailure::Refused, "invalid-fallback-protocol"))
 					},
 				},
-				None => Some(RequestFailure::Refused),
+				None => Some((RequestFailure::Refused, "unsupported-protocol")),
 			},
 		};
 
-		if let Some(error) = error {
-			self.metrics.register_outbound_request_failure(error.to_string().as_ref());
+		if let Some((error, reason)) = status {
+			self.metrics.register_outbound_request_failure(reason);
 			let _ = tx.send(Err(error));
 		}
 	}