As stated [here](https://docs.ray.io/en/latest/tune/api_docs/suggestion.html#concurrencylimiter-tune-suggest-concurrencylimiter), Bayesian optimization doesn't parallelize well and thus needs a `ConcurrencyLimiter`. Need to add it to the code examples [here](https://docs.ray.io/en/master/tune/examples/bayesopt_example.html) and [here](https://docs.ray.io/en/latest/tune/api_docs/suggestion.html#bayesian-optimization-tune-suggest-bayesopt-bayesoptsearch).