feat(config): integrate etcd for service discovery and config management

- Add etcd-client dependency for distributed configuration storage
- Implement EtcdConfig with priority: etcd > environment variables > defaults
- Add ServiceRegistry for service registration with lease keep-alive
- Integrate etcd-based service discovery for appks gRPC connections
- Add service watcher for real-time service instance updates
- Migrate Redis configuration from single URL to cluster node list
- Update Dockerfile with default IMKS_HOST and IMKS_PORT environment variables
- Add etcd bootstrap configuration through environment variables
- Implement Redis cluster URL building with optional authentication

telemetry/metrics.rs

@@ -2,11 +2,11 @@
 
 use std::sync::OnceLock;
 
+use opentelemetry::KeyValue;
 use opentelemetry::global;
 use opentelemetry::metrics::{Counter, Histogram, Meter, UpDownCounter};
-use opentelemetry::KeyValue;
-use opentelemetry_sdk::metrics::SdkMeterProvider;
 use opentelemetry_sdk::Resource;
+use opentelemetry_sdk::metrics::SdkMeterProvider;
 use prometheus::{Encoder, Registry, TextEncoder};
 
 use crate::ImksResult;
@@ -47,7 +47,9 @@ pub fn init_metrics(
     let exporter = opentelemetry_prometheus::exporter()
         .with_registry(registry)
         .build()
-        .map_err(|e| crate::ImksError::Internal(format!("failed to build Prometheus exporter: {e}")))?;
+        .map_err(|e| {
+            crate::ImksError::Internal(format!("failed to build Prometheus exporter: {e}"))
+        })?;
 
     let provider = SdkMeterProvider::builder()
         .with_resource(resource.clone())
@@ -153,7 +155,9 @@ impl MetricsInstruments {
 ///
 /// Encodes the Prometheus text format from the shared registry.
 pub async fn metrics_handler() -> actix_web::HttpResponse {
-    let registry = PROMETHEUS_REGISTRY.get().expect("Prometheus registry not initialized");
+    let registry = PROMETHEUS_REGISTRY
+        .get()
+        .expect("Prometheus registry not initialized");
 
     let metric_families = registry.gather();
     let encoder = TextEncoder::new();