Remove implementation of coroutine scope in generated services

[marcoferrer]

Implementing CoroutineScope in the generated services has proven to cause too many issues with ambiguous context / scope resolution.

Classes implementing CoroutineScope should have their life cycle bound to the start and stop of the unit of work they represent. Since service implementations generally have a life cycle that spans the life of the application, this makes them an Ill fit for implementing coroutine scope.

The original intent of implementing CoroutineScope was to give services a mechanism to provide an initial coroutine context for rpc calls. That initial context would be used to create a proper scope per rpc method invocation.

This pr introduces a new interface for services to implement that will still allow configuration of the initial rpc context. It will also allow less error prone usages of coroutines in service instances