[stable2412] Backport #7133: Sufix litep2p to the identify agent version for visibility (#7153)

Backport #7133 into `stable2412` from lexnv.

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Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

prdoc/pr_7133.prdoc

+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Sufix litep2p to the identify agent version for visibility
+
+doc:
+  - audience: [Node Dev, Node Operator]
+    description: |
+      This PR adds the `(litep2p)` suffix to the agent version (user agent) of the identify protocol.
+      The change is needed to gain visibility into network backends and determine exactly the number of validators that are running litep2p.
+      Using tools like subp2p-explorer, we can determine if the validators are running litep2p nodes.
+
+crates:
+- name: sc-network
+  bump: patch

substrate/client/network/src/litep2p/discovery.rs

@@ -246,7 +246,7 @@ impl Discovery {
 		_peerstore_handle: Arc<dyn PeerStoreProvider>,
 	) -> (Self, PingConfig, IdentifyConfig, KademliaConfig, Option<MdnsConfig>) {
 		let (ping_config, ping_event_stream) = PingConfig::default();
-		let user_agent = format!("{} ({})", config.client_version, config.node_name);
+		let user_agent = format!("{} ({}) (litep2p)", config.client_version, config.node_name);
 
 		let (identify_config, identify_event_stream) =
 			IdentifyConfig::new("/substrate/1.0".to_string(), Some(user_agent));