[core][oom] add debug guide for oom issues, include old policy as backup if default policy doesn't work

[clarng]

Description

Add more oom docs

• add guide to debug memory issues
• describe lifo policy, as backup when group-by fails the workload

Link

No response

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[stale]

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[stale]

Hi again! The issue will be closed because there has been no more activity in the 14 days since the last message.

Please feel free to reopen or open a new issue if you'd still like it to be addressed.

Again, you can always ask for help on our discussion forum or Ray's public slack channel.

Thanks again for opening the issue!