Added Material UI 4 import rule to plugins/apollo-explorer

Signed-off-by: Aditya Kumar <aditya.kumar60@infosys.com>

.changeset/mighty-fishes-wait.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-apollo-explorer': patch
+---
+
+Added an optional ESLint rule - no-top-level-material-ui-4-imports -in apollo-explorer plugin which has an auto fix function to migrate the imports and used it to migrate the Material UI imports for plugins/apollo-explorer.

plugins/apollo-explorer/.eslintrc.js

@@ -1 +1,5 @@
-module.exports = require('@backstage/cli/config/eslint-factory')(__dirname);
+module.exports = require('@backstage/cli/config/eslint-factory')(__dirname, {
+    rules: {
+      '@backstage/no-top-level-material-ui-4-imports': 'error',
+    },
+  });

plugins/apollo-explorer/src/components/ApolloExplorerBrowser/ApolloExplorerBrowser.tsx

@@ -15,7 +15,10 @@
  */
 
 import React, { useState } from 'react';
-import { Divider, makeStyles, Tab, Tabs } from '@material-ui/core';
+import Divider from '@material-ui/core/Divider';
+import Tab from '@material-ui/core/Tab';
+import Tabs from '@material-ui/core/Tabs';
+import { makeStyles } from '@material-ui/core/styles';
 import { JSONObject } from '@apollo/explorer/src/helpers/types';
 import { ApolloExplorer } from '@apollo/explorer/react';
 import { Content } from '@backstage/core-components';