expose chain identifier as a metric (MystenLabs#11823)

## Description 

As title. This will be a useful thing to watch during testnet wipe

## Test Plan 

tested locally

---
If your changes are not user-facing and not a breaking change, you can
skip the following section. Otherwise, please indicate what changed, and
then add to the Release Notes section as highlighted during the release
process.

### Type of Change (Check all that apply)

- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes
Expose chain identifier as a metric

crates/mysten-metrics/src/lib.rs

@@ -309,8 +309,11 @@ impl RegistryService {
 
 /// Create a metric that measures the uptime from when this metric was constructed.
 /// The metric is labeled with the provided 'version' label (this should generally be of the
-/// format: 'semver-gitrevision').
-pub fn uptime_metric(version: &'static str) -> Box<dyn prometheus::core::Collector> {
+/// format: 'semver-gitrevision') and the provided 'chain_identifier' label.
+pub fn uptime_metric(
+    version: &'static str,
+    chain_identifier: &str,
+) -> Box<dyn prometheus::core::Collector> {
     let opts = prometheus::opts!("uptime", "uptime of the node service in seconds")
         .variable_label("version");
 
@@ -320,7 +323,7 @@ pub fn uptime_metric(version: &'static str) -> Box<dyn prometheus::core::Collect
         opts,
         prometheus_closure_metric::ValueType::Counter,
         uptime,
-        &[version],
+        &[version, chain_identifier],
     )
     .unwrap();
 

crates/sui-node/src/main.rs

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 use clap::Parser;
+use fastcrypto::encoding::{Encoding, Hex};
 use mysten_common::sync::async_once_cell::AsyncOnceCell;
 use std::path::PathBuf;
 use std::sync::Arc;
@@ -63,9 +64,6 @@ fn main() {
         metrics::start_prometheus_server(config.metrics_address)
     };
     let prometheus_registry = registry_service.default_registry();
-    prometheus_registry
-        .register(mysten_metrics::uptime_metric(VERSION))
-        .unwrap();
 
     // Initialize logging
     let (_guard, filter_handle) = telemetry_subscribers::TelemetryConfig::new()
@@ -102,15 +100,15 @@ fn main() {
 
     // Run node in a separate runtime so that admin/monitoring functions continue to work
     // if it deadlocks.
-    let node_one_cell = Arc::new(AsyncOnceCell::<Arc<sui_node::SuiNode>>::new());
-    let node_one_cell_clone = node_one_cell.clone();
+    let node_once_cell = Arc::new(AsyncOnceCell::<Arc<sui_node::SuiNode>>::new());
+    let node_once_cell_clone = node_once_cell.clone();
     let rpc_runtime = runtimes.json_rpc.handle().clone();
 
     runtimes.sui_node.spawn(async move {
         if let Err(e) = sui_node::SuiNode::start_async(
             &config,
             registry_service,
-            node_one_cell_clone,
+            node_once_cell_clone,
             Some(rpc_runtime),
         )
         .await
@@ -124,14 +122,28 @@ fn main() {
         }
     });
 
-    let node_one_cell_clone = node_one_cell.clone();
+    let node_once_cell_clone = node_once_cell.clone();
     runtimes.metrics.spawn(async move {
-        let node = node_one_cell_clone.get().await;
+        let node = node_once_cell_clone.get().await;
+        let chain_identifier = match node.state().get_chain_identifier() {
+            // Unwrap safe: Checkpoint Digest is 32 bytes long
+            Some(chain_identifier) => Hex::encode(chain_identifier.into_inner().get(0..4).unwrap()),
+            None => "Unknown".to_string(),
+        };
+
+        info!("Sui chain identifier: {chain_identifier}");
+        prometheus_registry
+            .register(mysten_metrics::uptime_metric(
+                VERSION,
+                chain_identifier.as_str(),
+            ))
+            .unwrap();
+
         sui_node::admin::run_admin_server(node, admin_interface_port, filter_handle).await
     });
 
     runtimes.metrics.spawn(async move {
-        let node = node_one_cell.get().await;
+        let node = node_once_cell.get().await;
         let state = node.state();
         loop {
             send_telemetry_event(state.clone(), is_validator).await;

crates/sui-proxy/src/main.rs

@@ -64,7 +64,7 @@ async fn main() -> Result<()> {
     let registry_service = metrics::start_prometheus_server(metrics_listener);
     let prometheus_registry = registry_service.default_registry();
     prometheus_registry
-        .register(mysten_metrics::uptime_metric(VERSION))
+        .register(mysten_metrics::uptime_metric(VERSION, "sui-proxy"))
         .unwrap();
     let app = app(
         Labels {