feat(kubernetes/resource-usage): k8s resource usage for cluster, node and namespace EE-3 EE-1112 (#5301)

* backported resource usage functionality from EE

* utilising view bound endpoint object instead of depracated EndpointProvider

* refactor flatmap

* addressed merge conflict issues

app/kubernetes/metrics/rest.js

@@ -24,6 +24,14 @@ angular.module('portainer.kubernetes').factory('KubernetesMetrics', [
             method: 'GET',
             url: `${url}/nodes/:id`,
           },
+          getPods: {
+            method: 'GET',
+            url: `${url}/namespaces/:namespace/pods`,
+          },
+          getNodes: {
+            method: 'GET',
+            url: `${url}/nodes`,
+          },
         }
       );
     };