feat(cluster): implement distributed clustering with etcd coordination

- Integrate etcd-client for distributed coordination and leader election
- Add remote client macros with proper formatting for all services
- Implement RequestMetrics for tracking RPC performance and errors
- Add rate limiting mechanism across all service endpoints
- Create ElectionRequest and ElectionResult message types for leader election
- Add role management with primary/replica switching capabilities
- Implement health checker with automatic failover detection
- Add repository count metrics for cluster monitoring
- Update Cargo.toml with etcd-client and dashmap dependencies
- Modify RepoEntry to include read_only flag for replica handling
- Implement should_accept_election logic to prevent duplicate elections
- Add RoleChangedEvent handling for cluster role updates

Cargo.toml

@@ -18,6 +18,8 @@ name = "gitks"
 [dependencies]
 moka = { version = "0.12", default-features = false, features = ["sync"] }
 serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+sha2 = "0.11"
 gix = { version = "0.84", default-features = false, features = ["serde", "blame", "sha256", "sha1", "tracing", "merge", "max-performance-safe", "revision"] }
 gix-archive = { version = "0.33", features = ["sha256","sha1","document-features"] }
 duct = { version = "1", features = [] }
@@ -35,6 +37,8 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 ractor = { version = "0.15.13", features = ["cluster","tokio_runtime","monitors","message_span_propogation","async-trait"]}
 ractor_cluster = { version = "0.15.13", features = ["async-trait"] }
 async-trait = "0.1.89"
+etcd-client = { version = "0.18.0", features = ["tls"] }
+dashmap = "6"
 [[bin]]
 name = "gitks"
 path = "main.rs"