Replace node polyfills configuration with dummy fallback

They removed default polyfills but some dependecies require those
so this replaces those modules.
See https://webpack.js.org/migrate/5/#clean-up-configuration

[MAILPOET-3214]

webpack.config.js

@@ -41,6 +41,9 @@ const baseConfig = {
       'node_modules',
       'assets/js/src',
     ],
+    fallback: {
+      fs: false,
+    },
     extensions: ['.js', '.jsx', '.ts', '.tsx'],
     alias: {
       'handlebars': 'handlebars/dist/handlebars.js',
@@ -56,9 +59,6 @@ const baseConfig = {
       'asyncqueue': 'vendor/jquery.asyncqueue.js',
     },
   },
-  node: {
-    fs: 'empty'
-  },
   plugins: [],
   module: {
     noParse: /node_modules\/lodash\/lodash\.js/,
@@ -351,6 +351,9 @@ const testConfig = {
       'blob$': 'blob-tmp/Blob.js',
       'wp-js-hooks': path.resolve(__dirname, 'assets/js/src/hooks.js'),
     },
+    fallback: {
+      fs: false,
+    },
   },
   externals: {
     'jquery': 'jQuery',