Add warning about creating Cartridge Controller in React component

[kronosapiens]

The Cartridge Controller docs warn users not to create Controller instances inside of React components, as this would lead to the Controller being re-created on page load, leading to connection and performance issues:

⚠️ Important: The ControllerConnector instance must be created outside of any React components. Creating it inside a component will cause the connector to be recreated on every render, which can lead to connection issues.

We should update the Starknetkit docs to include a similar warning.