Support request body

[fsuter]

The new version allows for choosing the method for the data request. In case of "POST", it would be nice to be able to pass a request body too.

[websi]

I also need this feature. This would reduce the complexity of integrating a GraphQL API.

[fsuter]

I made the change so that any of the request options from Guzzle HTTP can be used. Since svconnector is just a base, this will be "visible" only in the specific services. I will update all relevant services.