DEV: enable CORS to all CDN get requests from workbox. (#11896)

To prevent opaque cache files, now all the CDN files will be requested in 'cors' mode if the cdn_cors_enabled global setting is enabled. Before enabling the setting, should enable the cors in the CDN server by adding the response header `access-control-allow-origin: *` or `access-control-allow-origin: https://discourse.example.com.`

And other external file requests other than CDN will not be cached if the response type is opaque.

lib/tasks/javascript.rake

@@ -161,6 +161,10 @@ def dependencies
       destination: 'workbox',
       public: true,
       skip_versioning: true
+    }, {
+      source: 'workbox-cacheable-response/build/.',
+      destination: 'workbox',
+      public: true
     }, {
       source: '@popperjs/core/dist/umd/popper.js'
     }, {