Implement ask-and-tell interface for DEHB

[Bronzila]

Similar to SMAC, an ask-and-tell interface would make DEHB more flexible and potentially easier to use.

[eddiebergman]

Some extra comments thinking out it's use case. SMAC has some hidden bugs as ask() and tell() was sort of put in but not planned out for non-default use cases.

• If I tell() many times before starting optimization, these results are used.
  • Makes warmstarting any optimizer with tell() trivial.
• If I tell() during optimization but with a result that was not suggested by DEHB, how should it be used. What happens to the population? What if it's not in a fidelity bracket DEHB is aware of? If there's no good idea, better to explicitly error then.
  • Can share information between concurrent optimizers or self experimentation.
• If I ask() twice without any internal update, will I get the same suggestion? Can I get two different suggestions for better parallelization?
  • xs = [ask(), ask()] -> Two same suggestions
  • xs = ask(2) -> Two different suggestions