Otel's Method Name is different between gRPC and HttpJson

[lqiu96]

Discovered in the Otel Draft PR: https://github.com/googleapis/sdk-platform-java/pull/2500

The Method Name is different between the two transports: gRPC: Echo.Echo HttpJson: google.showcase.v1beta1.Echo/Echo.

I believe this is because of the different Regex Matchers used to extract the MethodName: gRPC: https://github.com/googleapis/sdk-platform-java/blob/7902a41c87240d607179d07c28cce462ea135c5f/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcCallableFactory.java#L69 HttpJson: https://github.com/googleapis/sdk-platform-java/blob/7902a41c87240d607179d07c28cce462ea135c5f/gax-java/gax-httpjson/src/main/java/com/google/api/gax/httpjson/HttpJsonCallableFactory.java#L58

We should be consistent and pick one way to display the method name.