fix(obs): label node-local metrics by server (#5465)

Add stable server labels to node-local Prometheus metrics and OTLP resource attributes so dashboards can distinguish per-node CPU, memory, host network, and internode traffic series.

Co-authored-by: heihutu <heihutu@gmail.com>

crates/obs/src/lib.rs

@@ -64,6 +64,7 @@ mod error;
 mod global;
 mod logging;
 pub mod metrics;
+mod node_identity;
 mod telemetry;
 
 pub use cleaner::*;