Make it possible to define a Placement resource with predicate which filters hosting clusters based on the number of hosted clusters running on the given hosting cluster. The thresholds should be configurable and the implementation should be generic enough so support the following use-cases:

Placement1 - only include hosting clusters which have 80 or less hosted control planes defined on them

Placement2 - only include hosting clusters which have 60 or less hosted control planes defined on them

Placement3 - only include hosting clusters which have 0 hosted control planes defined on them