Chat CommandRenderer does not handle custom callbacks properly

[sdirix]

Bug Description:

Steps to Reproduce:

1. Within an agent, return a CommandChatResponseContentImpl only defining a custom callback, e.g. new CommandChatResponseContentImpl(undefined, customCallback);
2. Observe that the command renderer is not invoked
3. Observe that CommandChatResponseContent.is() called on such an instance will return false

Expected behavior

1. The command renderer should be invoked
2. CommandChatResponseContent.is shall return true for such an instance without a command but with a custom callback