Define a scheme to use OpenAPI extension mechanisms for kpt functions

[natasha41575]

From @mengqiy's document:

We need to augment OpenAPI with additional semantics to provide more metadata:

1. The actual meaning of a field. I.e. field X in GVK Y is Z. e.g. Field .spec.selector in GVK core.v1.Service is a “label”.
2. The linkage between objects. I.e. field X in GVK Y references field Z in GVK W. e.g. Field .spec.containers.envFrom.configMapRef.name references filed .metadata.name in core.v1.ConfigMap.

Task is to define the scheme for this