feat: Add Kubernetes examples and update dependencies

- Add Kubernetes examples demonstrating deployment of various
  applications (PostgreSQL, Redis, generic). This improves the
  documentation and provides practical usage examples.
- Add `tokio` dependency for async examples. This enables the use
  of asynchronous operations in the examples.
- Add `once_cell` dependency for improved resource management in
  Kubernetes module. This allows efficient management of
  singletons and other resources.

examples/kubernetes/clusters/postgres.rhai

@@ -10,6 +10,35 @@ print("Creating Kubernetes manager for 'database' namespace...");
 let km = kubernetes_manager_new("database");
 print("✓ Kubernetes manager created");
 
+// Create the namespace if it doesn't exist
+print("Creating namespace 'database' if it doesn't exist...");
+try {
+    create_namespace(km, "database");
+    print("✓ Namespace 'database' created");
+} catch(e) {
+    if e.to_string().contains("already exists") {
+        print("✓ Namespace 'database' already exists");
+    } else {
+        print("⚠️ Warning: " + e);
+    }
+}
+
+// Clean up any existing resources first
+print("\nCleaning up any existing PostgreSQL resources...");
+try {
+    delete_deployment(km, "postgres-cluster");
+    print("✓ Deleted existing deployment");
+} catch(e) {
+    print("✓ No existing deployment to delete");
+}
+
+try {
+    delete_service(km, "postgres-cluster");
+    print("✓ Deleted existing service");
+} catch(e) {
+    print("✓ No existing service to delete");
+}
+
 // Create PostgreSQL cluster using the convenience method
 print("\nDeploying PostgreSQL cluster...");
 
@@ -19,6 +48,11 @@ try {
         "app": "postgres-cluster",
         "type": "database",
         "engine": "postgresql"
+    }, #{
+        "POSTGRES_DB": "myapp",
+        "POSTGRES_USER": "postgres",
+        "POSTGRES_PASSWORD": "secretpassword",
+        "PGDATA": "/var/lib/postgresql/data/pgdata"
     });
     print("✓ " + result);