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/Cargo.toml

@@ -39,6 +39,7 @@ log = "0.4"
 
 # Rhai scripting support (optional)
 rhai = { version = "1.12.0", features = ["sync"], optional = true }
+once_cell = "1.20.2"
 
 # UUID for resource identification
 uuid = { version = "1.16.0", features = ["v4"] }