Add ssl connection functionality

Hi, I added configuration options to use the AMQPSSL connection.

I am a bit unsure about the configuration.
First I didn't find a way to simply specify something like a generic associative array for the ssl_options. Those parameters are simply passed to stream_context_set_option. So I have looked all options up and specified them explicitly.
Additionally it is not possible to use now a "lazy ssl" connection as the dependency chain in php-amqplib doesn't provide this option. I think somehow an exception should be thrown when this happens to notify the user about potentially unexpected behavior. Tough I am not sure in which way this should be handled, do you know if Symfony provides such checks in the ConfigTreeBuilder?