fix: Address issues in OpenTelemetry audit exporter

HIGH:
- Fix test code compilation by using tuple indexing (.0, .1) for KeyValue
  attributes instead of struct field access
- Add endpoint URL validation using url::Url::parse() with error context
- Add HTTPS validation warning for insecure HTTP endpoints

MEDIUM:
- Replace Mutex with RwLock for logger_provider since emit() only requires
  read access, improving concurrent performance
- Add TLS requirements documentation in endpoint parameter docs
- Convert all synchronous tests to async with #[tokio::test] to satisfy
  gRPC client initialization requirements

Dependencies:
- Add url crate 2.5 for URL parsing and validation

Author: inureyes

Cargo.lock

@@ -72,6 +72,7 @@ serde_json = "1.0"
 opentelemetry = "0.21"
 opentelemetry_sdk = { version = "0.21", features = ["rt-tokio", "logs"] }
 opentelemetry-otlp = { version = "0.14", features = ["grpc-tonic", "logs"] }
+url = "2.5"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 security-framework = "3.5.1"