Things which we should be code-generating

[thockin]

1. k/k hack/lib/init.sh has KUBE_AVAILABLE_GROUP_VERSIONS which is a hand-maintained list of API groups
2. k/k pkg/api/testing/defaulting_test.go has typesWithDefaulting which is a hand-maintained list of GVKs with defaulters
3. k/k pkg/controlplane/instance.go has stableAPIGroupVersionsEnabledByDefault and betaAPIGroupVersionsDisabledByDefault and alphaAPIGroupVersionsDisabledByDefault which are hand-maintained
4. k/k staging/src/k8s.io/api/roundtrip_test.go has var groups = []runtime.SchemeBuilder which is hand-maintained