Provide ability to disable gRPC client(s) using properties

[asarkar]

I'd like to disable gRPC client(s) using properties, similar to that available for the server grpc.server.enabled=false. grpc.client.enabled=false would disable all gRPC client stub creation, and grpc.client.greeter.enabled=false would disable greeter client stub creation. The corresponding injection points (fields) would be Optional.empty or null if using Kotlin null type. If not Optional or null type, an exception would be thrown.

This allows for specific slices of the application to be tested. In my case, I've a client-A that calls service-A that calls client-B that calls external-service-B. Depending on the test scenario, I substitute in process versions for service-A and external-service-B to test the flow, or use the real ones.

What I'd like to do now is use the same test for calling service-A deployed in my integration environment. That means, I only need client-A, and service-A and client-B beans don't need to be created.

One way is to use Requires, but it makes the Production code coupled with test code, and also duplicates code.