Move kafka-grpc options for grpc to with section of config

[jfallows]

In general, the options and when sections of binding should describe concepts aligned with the origin type, such as kafka in the case of kafka-grpc, and the with section should describe concepts aligned with the routed type, such as grpc in the case of kafka-grpc.

We need to move the kafka-grpc options for scheme and authority to with section.