Dashboard for cuDF spilling

[pentschev]

When cuDF spilling is enabled we may eventually get allocation errors when 100% of the memory is unspillable. The information about cuDF spilling memory usage is very useful, but failures are perhaps delayed to a point where that information doesn't help us understanding why we got there.

With the above said, a dashboard that allows us to look at both cuDF's device memory consumption and spilled (host) memory usage in real-time would help us in understanding where we have pressure, allowing to see the history of cuDF memory usage is definitely a bonus as it would permit us seeing what happened even if workers die abruptly.

[quasiben]

Note, to get statistics for cuDF spilling the user needs to set an environment flag/config option:
https://docs.rapids.ai/api/cudf/stable/developer_guide/library_design/#statistics