Added possibility to decorate shell command

[nuvolapl]

Example

$builder = $this->getConfigBuilder();
$builder
    ->server(
        'user@host',
        [
            Server::ROLE_APP,
        ],
        [
            Property::command_decorator => function (Server $server, string $shellCommand, array $envVars) {
                return \sprintf("sudo chroot /srv/app/ bash -c '%s'", $shellCommand);
            },
        ]
    )
;

... will execute: ssh user@host 'sudo chroot /srv/app/ bash -c \'echo "hello"\''