feat: add eslint rule for top level imports

Signed-off-by: Timothy Deakin <cftad@protonmail.com>

.changeset/smooth-spoons-repeat.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-azure-sites': patch
+---
+
+Added the `no-top-level-material-ui-4-imports` ESLint rule to aid with the migration to Material UI v5

plugins/azure-sites/.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/azure-sites/src/components/AzureSitesOverviewTableComponent/AzureSitesOverviewTable.tsx

@@ -15,17 +15,15 @@
  */
 
 import React, { Dispatch, useEffect, useState } from 'react';
-import {
-  Box,
-  Card,
-  Chip,
-  IconButton,
-  LinearProgress,
-  Menu,
-  MenuItem,
-  Snackbar,
-  Tooltip,
-} from '@material-ui/core';
+import Box from '@material-ui/core/Box';
+import Card from '@material-ui/core/Card';
+import Chip from '@material-ui/core/Chip';
+import IconButton from '@material-ui/core/IconButton';
+import LinearProgress from '@material-ui/core/LinearProgress';
+import Menu from '@material-ui/core/Menu';
+import MenuItem from '@material-ui/core/MenuItem';
+import Snackbar from '@material-ui/core/Snackbar';
+import Tooltip from '@material-ui/core/Tooltip';
 import { default as MuiAlert } from '@material-ui/lab/Alert';
 import {
   AzureSite,