Benchmarking and performance optimization

[edsko]

Some references:

• https://grpc.io/docs/guides/performance/
• https://grpc.io/docs/guides/benchmarking/
• https://ably.com/blog/grpc-stream-performance

Marked this as low priority as grapesy is high throughput is not of the essence for current grapesy deployments.

[edsko]

I think once #162 is resolved, we have sufficient benchmarks to show that grapesy performs rather well.

[edsko]

The plan here is to close this ticket after Finley compares the kvstore benchmark in 6 variations:

• sequential protobuf, linux/osx
• concurrent protobuf, linux/osx
• concurrent JSON, linux/osx

[edsko]

Let's make sure that #192 is done before running the benchmarks.