[Feature Request] Support optuna 2.8.0

[nikvaessen]

🚀 Feature Request

I would like to make use of the constant_liar parameter of TPESampler which was added in version 2.8.0. This is helpful for preventing sampling around the same neighborhood when n_jobs is larger than 1.

Motivation

Currently the optuna sweeper is restricted to version <2.5.0 as per https://github.com/facebookresearch/hydra/blob/9e3a5261a91febb028fb16613b4bead535c08277/plugins/hydra_optuna_sweeper/setup.py#L31

Additional context

What is the reason for requiring this specific version of Optuna?

[nikvaessen]

I see this is already being worked on https://github.com/facebookresearch/hydra/pull/1726

[omry]

I don't believe there is a plan to add functionality as a part of #1726. Once it's done feel free to send a followup pull request to add what you need.