argon2: add benchmarks using criterion

[dyc3]

I added some benchmarks using the criterion crate. The reason I chose to include criterion is because it makes it easier to determine if a change has a statistically significant impact.

I'm not really sure which benchmarks will produce good signal for us, so the parameters will probably need to be tweaked before merging. I'm open to suggestions.

[newpavlov]

I would prefer to keep criterion benchmarks in a separate crate as we do in the stream ciphers repository to prevent criterion being pulled in our CI jobs.