use istio client-go library instead of knative (#1661)

use istio client-go library instead of knative
bump kubernetes dependency version
change code coverage to codecov

vendor/k8s.io/client-go/pkg/apis/clientauthentication/OWNERS

@@ -1,3 +1,5 @@
+# See the OWNERS docs at https://go.k8s.io/owners
+
 # approval on api packages bubbles to api-approvers
 reviewers:
 - sig-auth-authenticators-approvers

vendor/k8s.io/client-go/pkg/apis/clientauthentication/v1alpha1/types.go

@@ -22,7 +22,7 @@ import (
 
 // +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
 
-// ExecCredentials is used by exec-based plugins to communicate credentials to
+// ExecCredential is used by exec-based plugins to communicate credentials to
 // HTTP transports.
 type ExecCredential struct {
 	metav1.TypeMeta `json:",inline"`