Iteration configuration: end-to-end experience

[nth-commit]

We want to be able to have precise control over the number of iterations we run our test with.

However, we also want to have global configuration. For example, I might want to do 10 iterations of my tests locally (for quicker feedback), but 100 iterations on CI.

Some tests might be more performance heavy, so we would ideally reduce them by a factor, and have that reduction be proportioned out the same way for CI vs local.