refactor(agent): refactor volume browser to es6 (#4086)

* refactor(agent): replace root with index

* refactor(agent): use simple export

* refactor(agent): replace function with class

* refactor(agent): replace promise with async

app/agent/components/volume-browser/index.js

@@ -0,0 +1,13 @@
+import angular from 'angular';
+
+import { VolumeBrowserController } from './volumeBrowserController';
+
+angular.module('portainer.agent').component('volumeBrowser', {
+  templateUrl: './volumeBrowser.html',
+  controller: VolumeBrowserController,
+  bindings: {
+    volumeId: '<',
+    nodeName: '<',
+    isUploadEnabled: '<',
+  },
+});