Add wandb logging support to Trainer class

[janosh]

@BowenD-UCB let me know if you'd like to review this

here's the run metadata that's recorded by default

[BowenD-UCB]

Thanks for the implementation!
I can take a look into the wandb logger later, I assume it's already working well on your side?
Is it possible to add some test to this?

[janosh]

I can take a look into the wandb logger later, I assume it's already working well on your side?

yes

Is it possible to add some test to this?

i did in e7ef618. happy to add more if we can think of good tests.

EDIT: extended the test coverage to extra_run_config in bc87fd0