[Feature] Expose additional arguments for Wandb

[Xmaster6y]

What does this PR do?

It exposes wandb_extra_kwargs in the experiment config to pass additional arguments to both WandbLogger and wandb.init.

To discuss

• Should there be an extra validation in ExperimentConfig, e.g. using a field like:

@dataclass
class WandbExtraKwargs:
    """
    Extra kwargs for wandb.
    """
    # WandbLogger
    offline: bool = False
    ...
    # wandb.init
    entity: Optional[str] = None
    ...

• Is having wandb as a default logger (base_experiment) really ideal?

Happy to iterate.

[matteobettini]

This looks great, sorry for taking so long. Only one point about bc-breaking

[matteobettini]

So the only problem is that this is backwards compatibility breaking and I would like to avoid that.

What about we keep the project name out and have wandb_extra_kwargs: {}?

Then is someone provides the project in wandb_extra_kwargs and it is different from project_name we tell them through an error

[Xmaster6y]

I get you, sounds good.