Support variable in HTTP Service

[floyd-fuh]

It would be convenient to have a global variable, let's say with the value "test.example.org", that is then accepted in the HTTP service (where the request should be sent to). Because if you switch the environment, let's say to "integration.example.org", you only need to change the global variable.

It already works for Host header, so I just need it to work for the HTTP service as well. If that would only accept global variables that would probably be enough.