feat: add feature flag for separate weekly-random prune and check

[shreddedbacon]

The current K8UP_WEEKLY_RANDOM_FEATURE_FLAG variable impacts both prune and check, so this should be phased out in favour of the new ones that leverage the actual supported featureflag support

LAGOON_FEATURE_FLAG(_FORCE|_DEFAULT)_K8UP_WEEKLY_RANDOM_CHECK
LAGOON_FEATURE_FLAG(_FORCE|_DEFAULT)_K8UP_WEEKLY_RANDOM_PRUNE

Setting these as global scope vars with the value enabled turns on the @weekly-random schedule for either check or prune

• https://docs.k8up.io/k8up/2.10/references/schedule-specification.html

[shreddedbacon]

since this is a relatively harmless change, i'm going to merge it.

most of the minor diffs are just formatting changes, the bulk of the changes just use an OR to check if one flag or the other are set and the functionality of the templating is mostly unchanged