Benchmark: Multiple UDP clients and servers

[markmandel]

The other thought I had too was it might be worth doing benchmarks with multiple udp clients (maybe more than current cpu on the machine?) and multiple servers, and look at the same things.

I think this would be a good variable to benchmark

Originally posted by @XAMPPRocky in https://github.com/googleforgames/quilkin/issues/479#issuecomment-1029219531