Added Material UI 4 import rule to plugins/playlist

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

.changeset/purple-bananas-add.md

@@ -2,4 +2,4 @@
 '@backstage/plugin-playlist': patch
 ---
 
-Added an optional ESLint rule - no-top-level-material-ui-4-imports - in Playlist plugin which has an auto fix function to migrate the imports and used it to migrate the Material UI imports for `plugins/playlist`.
+Adjusted MUI imports for better tree shaking.

plugins/playlist/.eslintrc.js

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