Bazel: Raw Services

[sgammon]

After #271, figure out how to integrate raw services in the same way. This is slightly more complex, because we have to invoke grpc-web, but there is apparently support for this in stackb's fork of rules_proto. Reach goal for 1.6.1.

[Yannic]

In case you didn't know, there is support for Bazel / rules_closure in the gRPC-web repo, and it will be switched to rules_proto after grpc/grpc-web#575. So it should just work for you.

[sgammon]

Thank you @Yannic! I didn't know that, and yes, that does sound like it would work perfectly. I'll keep an eye on that issue.