Provide more details when the command does not exist

[pPrecel]

Description

Users should be informed when a wrong command that does not exist is called (for example for an extension that is not installed)

Actual result

When we call the what-is-this command that doesn't exist we should be informed that this command is not found. Instead of this, we print help:

kyma@v3 alpha what-is-this
A set of alpha prototypes that may still change. Use in automations on your own risk

Usage:
  kyma alpha [command]

Available Commands:
  access             Produce a kubeconfig with Service Account based token and certificate
  app                Manage applications on Kubernetes cluster
  hana               Manage a Hana instance on the Kyma platform
  module             Manage kyma modules
  oidc               Create kubeconfig with an OIDC token
  provision          Provisions a Kyma cluster on the BTP
  reference-instance Add an instance reference to a shared service instance

Flags:
      --kubeconfig string       Path to the Kyma kubeconfig file
      --show-extensions-error   Print possible error when fetching extensions failed

Global Flags:
  -h, --help   Help for the command

Use "kyma alpha [command] --help" for more information about a command.

Expected result

kyma@v3 alpha what-is-this
unknown command "what-is-this" for "kyma alpha"