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.

kubernetes/tests/rhai/run_all_tests.rhai

@@ -8,8 +8,9 @@ print("");
 // Test configuration
 let test_files = [
     "basic_kubernetes.rhai",
-    "namespace_operations.rhai", 
-    "resource_management.rhai"
+    "namespace_operations.rhai",
+    "resource_management.rhai",
+    "env_vars_test.rhai"
 ];
 
 let passed_tests = 0;
@@ -63,7 +64,8 @@ let required_functions = [
     "delete",
     "pod_delete",
     "service_delete",
-    "deployment_delete"
+    "deployment_delete",
+    "deploy_application"
 ];
 
 let registered_functions = 0;
@@ -76,7 +78,11 @@ for func_name in required_functions {
 print("");
 print("=== Summary ===");
 print("Required functions: " + registered_functions + "/" + required_functions.len());
-print("Basic validation: " + (passed_tests > 0 ? "PASSED" : "FAILED"));
+if passed_tests > 0 {
+    print("Basic validation: PASSED");
+} else {
+    print("Basic validation: FAILED");
+}
 print("");
 print("For full testing with a Kubernetes cluster:");
 print("1. Ensure you have a running Kubernetes cluster");