gRPC reflection v1 support

[wvuong]

Motivation:

Add support for the gRPC reflection api which is commonly used by gRPC tooling like Postman, Insomnia, k6, grpcurl for service discovery and transcoding. Fixes #22

• Added the v1 reflection.proto from gRPC
• Updated pom.xml to compile reflection.proto
• Added GrpcServerIndex which contains service descriptors
• Added ReflectionServiceV1Handler which is a Vertx gRPC handler for handling reflection requests
• Added ReflectionServiceV1Test to test and demonstrate usage

Conformance:

Eclipse Contributor Agreement signed.

[vietj]

can we try to make this work for vertx-grpc-server as well ?

[wvuong]

Yes, we have that working on the 4.x branch at my job. However for 5.x, GrpcServerIndex is dependent on a few classes from io.grpc:grpc-api to parse out the service descriptors. And it looks like you are trying to keep a separation and don't want to add io.grpc:grpc-api as a direct dependency in vertx-grpc-server...

Perhaps this is better as a new submodule in the project so that people can use it with vertx-grpc-server or vertx-grpcio-server?

[vietj]

which API is necessary ? vertx has its own generator so perhaps we can have this working as well using the generator.

[vietj]

I think I will merge it as is and take it from here as I need it with pure gRPC to build JPMS/gRPC example

[wvuong]

for GrpcServerIndex

import io.grpc.ServerServiceDefinition;
import io.grpc.ServiceDescriptor;

from io.grpc:grpc-api

[vietj]

I think actually for now what we are missing is documentation, can you add this ? it is very important

[wvuong]

I can update ioserver.adoc and add an example tonight

[vietj]

thanks @wvuong