Add GPU availability endpoint for providers

[nickpetrovic]

Resolve BE-1499

[nickpetrovic]

@luke-lombardi @jsun-m Could use some thoughts/opinions on whether or not machines should be an abstraction. Should we consider a new category?

~Oh just FYI I still need to test the abstraction.~

[nickpetrovic]

~Example of one can use this in their handler code.~

@endpoint()
def func():
    gpus = machines.gpus_available()
    print(f"{gpus=}")
    return {"gpus": gpus}

EDIT: We're no longer going to have an abstraction for this.