Console command as service

| Q             | A 
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.4+
| Fixed tickets | N/A
    
Command as a service can be useful to give access to services and
configuration parameters in the `configure` method.

A simple use case: you want to allow the user to set an option's default
value in the `app/config/parameters.yml` file. Or the default value
needs to be computed by  a service (database retrieval for instance).
    
With a `ContainerAwareCommand`, this wouldn't be possible because the
`configure` method is called from the constructor, so the container
isn't set yet.