update reflection.proto from v1alpha to v1

[JamesNK]

See #1825 and its discussion.

No other languages have been updated to v1 yet. We should wait until there is a plan.

[JamesNK]

More discussion: grpc/grpc#27957

[HaydnDias]

Hey, was wondering if it's worth revisiting this? We've started implementing gRPC api's in .net, and have found a bunch of the tooling only supports v1 reflection these days (k6, grpcurl, postman also have recently stated they intend to move to v1 (with fallback).

[prcstak]

We're also using gRPC in .NET, and while v1alpha works, we constantly see Service 'grpc.reflection.v1.ServerReflection' is unimplemented in the logs. Seems like it's time to switch to full v1 reflection.