adding rollbar plugin & backend

This is the first commit of the rollbar plugin. It is fully functional
but will require some additional features to make it more usable and
feature complete. It currently includes a backend wraps the rollbar REST
API and provides data for the frontend plugin.

plugins/rollbar/dev/index.tsx

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { createDevApp } from '@backstage/dev-utils';
+import { plugin } from '../src/plugin';
+
+createDevApp().registerPlugin(plugin).render();