Add rustls-rustcrypto as one of the benchmarked providers

[stevefan1999-personal]

Coming from rustls/rustls#1763 (comment), I think this is an interesting way to compare the performance of different providers.

[cpu]

Hi @stevefan1999-personal,

I suspect there are going to be more and more providers over time. I'm worried that adding one external provider to our benchmarks would motivate adding each new one that shows up, inflating both runtime and maintenance costs.

Could the Rust Crypto project could consider running their own benchmarks? Our tooling is open source and doesn't necessarily have to be run as part of a GitHub application integration - it can be used for one-off benchmarking as well.