GUACAMOLE-773: Add license information for new JavaScript dependencies pulled in by Webpack.

doc/licenses/webpack-4.46.0/README

@@ -0,0 +1,8 @@
+Webpack (https://webpack.js.org/)
+---------------------------------
+
+    Version: 4.46.0
+    From: 'JS Foundation and other contributors'
+    License(s):
+        MIT (bundled/webpack-4.46.0/LICENSE)
+