Consider support gRPC server reflection

[spericas]

Problem Description

gRPC tools such as grpcurl can take advantage of server reflection to avoid the need to specify a proto file (or equivalent compiled representation) when interacting with a Helidon-based gRPC service. For example, in order to access our RandomService example, the proto param is required as shown next:

>> grpcurl -d '{ "number": 100 }' -proto src/main/proto/random.proto \
      -insecure localhost:8080 RandomService/RandomSingle 
{
  "number": 95
}

With support for server reflection, the proto information will be automatically discovered at runtime, simplifying the use of tools like this. More information about server reflection available here.