Add arguments to enable cuDF spilling and set statistics

[pentschev]

Add arguments to enable cuDF spilling and set statistics in dask cuda worker/LocalCUDACluster. This is implemented as a Dask plugin, and does not require users anymore to rely on client.run to do that.

Closes #1280

[rjzamora]

Thanks for this @pentschev ! Only one minor comment/question from me.

Side thought: We have a lot of options at this point. Do you think it makes sense to deprecate anything?

[rjzamora]

Is there any way to detect if the user is doing this and warn/raise? This doc-string is good, but I'm sure some users will never read it :)

[pentschev]

Warning added in d7ffa0a . @madsbk do you think we should just raise a warning or raise a warning and disable JIT-Unspill regardless of the user enabling both together, i.e., --enable-cudf-spill --enable-jit-unspill would emit a warning saying JIT-Unspill has been disabled and only cuDF spill will be active?

Side thought: We have a lot of options at this point. Do you think it makes sense to deprecate anything?

Probably @madsbk also has a better sense of that as well, do you have thoughts on this?

[madsbk]

I think we should raise a warning only.

Side thought: We have a lot of options at this point. Do you think it makes sense to deprecate anything?

I think we should wait a bit with deprecating until we get a good solution from the NO-OOM work.

[madsbk]

Thanks @pentschev, looks good

[pentschev]

Thanks @rjzamora and @madsbk for reviewing!

[pentschev]

/merge