Docs: Enhance "Scheduling and Autoscaling" with details on Counts and Lists

[markmandel]

Depends on:

• #3649

Will need a section in Scheduling and Autoscaling covering how counts and lists impacts all aspects of Autoscaling, Fleet scale down, and Allocation prioritisation.

This is covered pretty well by the above documentation, but it should be covered in both places - or at least linked? (I lean towards duplicated content).

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[markmandel]

This has been on my plate for a while. I should get to this.