CRUD APIs for Istio resources (istio#54)

Author: nacx

tsb/private/v2/cluster_service.pb.go

@@ -29,6 +29,9 @@ service Cluster {
   };
 
   rpc GetCluster(GetClusterRequest) returns (tsb.v2.Cluster) {
+    option (tetrateio.api.tsb.private.v2.requires) = {
+      permissions: READ
+    };
     option (google.api.http) = {
       get: "/v1/{fqn=tenants/*/clusters/*}"
     };