Add support for generating gRPC service code for Runtime pseudo nodes

[conradgrobler]

The OakServiceGenerator generates code for use by WASM modules, but the generated code requires a reference to the SDK to compile. We should implement a version that generates gRPC service code that can be used by pseudo nodes in the runtime.

[daviddrysdale]

@conradgrobler is this now fixed?

[conradgrobler]

I don't think it is fixed. The main event loop and the matching on method_name is still manually done in the Roughtime pseudo node. If there is support for generating the code automatically I am not aware of it.

[daviddrysdale]

Ah OK, I misunderstood – I thought this just covered the generated service code doing use oak;.