Add benchmark scenarios to illustrate where Request Queuing benefits

Epic https://github.com/aspnet/AspNetCore/issues/10702

In general, we need scenarios that trigger thread-pool starvation (blocking thread-pool threads is the most common trigger). We suspect that I/O bound work won't necessarily improve RPS, but would improve memory usage. CPU bound work would likely improve RPS by reducing thread context switches.

We should evaluate both kinds of scenarios (I/O bound can be simulated with `Thread.Sleep`, CPU bound can be simulated by spinning the CPU).