add fetching into discovery client for OpenAPI v3

reflect latest struct changes

use correct discovery openapi test data layout

make the OpenAPIv3 interface less blue

field grouping

add copyrights

implement cached discovery client

add cached discovery tests

address review feedback

Kubernetes-commit: 075866b3e3ea029c243d82d8d6eb99e96d9c49d3

restmapper/discovery_test.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/apimachinery/pkg/runtime/schema"
 	"k8s.io/apimachinery/pkg/version"
 	. "k8s.io/client-go/discovery"
+	"k8s.io/client-go/openapi"
 	restclient "k8s.io/client-go/rest"
 	"k8s.io/client-go/rest/fake"
 
@@ -417,6 +418,10 @@ func (*fakeFailingDiscovery) OpenAPISchema() (*openapi_v2.Document, error) {
 	panic("implement me")
 }
 
+func (c *fakeFailingDiscovery) OpenAPIV3() openapi.Client {
+	panic("implement me")
+}
+
 type fakeCachedDiscoveryInterface struct {
 	invalidateCalls int
 	fresh           bool
@@ -490,6 +495,10 @@ func (c *fakeCachedDiscoveryInterface) OpenAPISchema() (*openapi_v2.Document, er
 	return &openapi_v2.Document{}, nil
 }
 
+func (c *fakeCachedDiscoveryInterface) OpenAPIV3() openapi.Client {
+	panic("implement me")
+}
+
 var (
 	aGroup = metav1.APIGroup{
 		Name: "a",