Add support for guzzle/guzzle-services

[csarrazi]

Support for guzzle-services was dropped in branch 2.0 as the library was not updated yet to handle version 6.x of Guzzle. As this was fixed in the last months, we can now resume support for guzzle-services in the upcoming versions of the bundle.

[andreicio]

I could work on this, since I integrated csa with guzzle-services on my project, but I need to understand how you would like this to work.

[csarrazi]

You could take a look at branch 1.x, where this was implemented at the time :)

That should give you some idea of the way Guzzle service definition files could be defined, and the client wrapped by guzzle-services.

In any case, as this feature was removed from the bundle, it can actually be re-added in a completely new fashion, so I'm open to all suggestions!