Document example of running Cubed on Ray managed by Skypilot

[alxmrs]

As an alternative to AWS, I bet we could run Ray managed on a "neo cloud" by using Skypilot. See these docs:

• https://docs.skypilot.co/en/latest/running-jobs/distributed-jobs.html#executing-a-distributed-ray-program
• https://docs.skypilot.co/en/latest/examples/auto-failover.html (scarce resources could be GPUs/TPUs or high count CPU machines).

CC: @Michaelvll, @romilbhardwaj

xref: #769, #488.

[romilbhardwaj]

This is a great idea - SkyPilot can help users easily launch Ray clusters on any infra. Perhaps the ray executor backend in cubed could run on top of the Ray cluster provisioned via SkyPilot?