Allow to specify method on receiver service tag

[diimpp]

Hi,

would be cool to be able to specify which method should handle message processing.

Like so

my_receiver:
    class: Acme\Receiver
    # public: true # Make sure the service is public
    tags:
         - { name: bernard.receiver, message: SendNewsletter, method: sendMyNewsletter }
         - { name: bernard.receiver, message: ImportUsers }