grpc-benchmark: add generated code and TLS certificates

[arjan-bal]

Addresses: #2666

This PR add the proto files and TLS certificates required to run the gRPC benchmarks.

The proto files are copied from the grpc-proto repository.

The TLS certs are copied from the gRPC Go repo which seem to be copied from the core repo.

[ejona86]

It seems like files are missing; I don't see the actual benchmark workers.

[arjan-bal]

It seems like files are missing; I don't see the actual benchmark workers.

Now I've copied all the files over from https://github.com/grpc/grpc-proto/blob/master/grpc/testing, except test.proto which seems to be used for xDS tests. The worker service is defined in grpc-benchmark/proto/grpc/testing/worker_service.proto.

[arjan-bal]

While working on the worker implementation, I realized that we need a worker server (not a client), so I switched to generating the worker service code for Tonic.

[ejona86]

I still don't understand this PR. How does this fix #2666? I don't see any client/server code that implements any functionality.

[arjan-bal]

This is the first in a series of PRs addressing #2666. I intentionally used "Addresses" instead of "Fixes" so GitHub links the PR without automatically closing the issue.

I originally drafted the benchmarking binary using tonic clients and servers last year (see arjan-bal#1). To make the code easier to review, I'm splitting the changes into self-contained parts. The next PR in the chain, which contains the worker and benchmark server implementation, is #2706.

[ejona86]

But "addresses" means the same as "fixes" in this context, as it implies completion. So this specific PR is not addressing the issue. I typically see language like "contributes to" or "as part of addressing" for this sort of thing. (The README was similarly misleading in that it said it contained the implementations.)

[ejona86]

Fix the "addresses" language to make clear this is only the first piece.

[ejona86]

What is server.key? Should this be server1.key? I don't see how someone would know that these are specific shared files, especially if they are renamed. We need some documentation saying this is a copy from grpc/src/core/tsi .