fix code generation for CRDs with recursive schema fields

[ilackarms]

currently, SKv2 will crash with a stack overflow if a user tries to generate manifests for CRDs whose schemas contain recursive fields (fields that reference a parent type, allowing recursion).

this is an inherent limitation of kubernetes, which does not support references in the CRD's openapi validation schema: kubernetes/kubernetes#62872

recursive references cannot be expanded infinitely, although cue will attempt to do so when generating with our current implementation, which prevents crd manifest generation from being able to finish (ending with stack overflow crash).

the most obvious workaround for this problem would be to disable validation for the entire CRD; however this is problematic as a number of CRDs in gloo-mesh would be affected. the next best workaround would be to disable validation for the specific recursive fields within the openapi schema.

implementing this will require changes to cue as well as the skv2 code which leverages it.