exec credential provider: add ProxyURL to Cluster

Signed-off-by: Andrew Keesler <[email protected]>

Author: ankeesler

keps/sig-auth/541-external-credential-providers/README.md

@@ -271,6 +271,10 @@ type Cluster struct {
   // +listType=atomic
   // +optional
   CAData []byte `json:"caData,omitempty"`
+  // ProxyURL is the URL to the proxy to be used for all requests to this
+  // cluster.
+  // +optional
+  ProxyURL string `json:"proxy-url,omitempty"`
   // Config holds additional config data that is specific to the exec plugin
   // with regards to the cluster being authenticated to.
   // +optional