Allow to disable cluster schema validation on sylva-units HelmRelease

Summary

sylva-capi-cluster is now extendable, but the schema is imported in sylva-core which forbid to extend sylva-capi-cluster without overwriting sylva-core schema.

We should add a parameter in .Values to skip the validation at sylva-units level.

Details

Allow any object in cluster definition if skip_cluster_check is true