Configuration API v1: SP support

Adding the first version of the configuration API to get SP configuration to the Gateway
The command has just a JSON blob, not a structured body. That is kinda hard to validate wiht the SF validator, which expects objects. Besides that, the validation is now done eagerly, throwing an exception on the first invalid value. Once we get the lazy assertions it might be more feasible to do actual validation, returning all errors at once. For now this is i.m.o. the best solution given the tools we have. It is planned to revisit this once we have lazy assertions though.