Cronjob to prune unused rendered MachineConfigs

[haasad]

Adds a cronjob to regularly (once a week) prune unused rendered machineconfigs. Uses oc adm prune renderedmachinconfigs as described in https://docs.openshift.com/container-platform/4.16/machine_configuration/machine-configs-garbage-collection.html#machine-configs-garbage-collection

Instead of pruning all unused rendered machineconfigs we keep the 5 most recent rendered machineconfigs for each machineconfigpool. This is useful for debugging issues and tasks like https://kb.vshn.ch/oc4/how-tos/force-reboot.html

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[github-actions]

🚀 This PR has been released as v4.4.0

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