FEATURE: Normalize the service worker route (#8359)

* FEATURE: Normalize the service worker route

Update cache headers so they are not immutable outside of the rails app

Add the ability to purge the service worker cache from localhost

Rails -> nginx will pass immutable flags so the file is cached until reloaded.
In most cases, nginx will have its cache flushed on rebuild (new image)

For those needing dynamic re-caching (such as upgrading via the UI),
a rake task for flushing the service worker script is provided
through `assets:flush_sw`

lib/tasks/assets.rake

@@ -68,6 +68,19 @@ task 'assets:precompile:css' => 'environment' do
   end
 end
 
+task 'assets:flush_sw' => 'environment' do
+  begin
+    hostname = Discourse.current_hostname
+    default_port = SiteSetting.force_https? ? 443 : 80
+    port = SiteSetting.port.to_i > 0 ? SiteSetting.port : default_port
+    STDERR.puts "Flushing service worker script"
+    `curl -s -m 1 --resolve '#{hostname}:#{port}:127.0.0.1' #{Discourse.base_url}/service-worker.js > /dev/null`
+    STDERR.puts "done"
+  rescue
+    STDERR.puts "Warning: unable to flush service worker script"
+  end
+end
+
 def assets_path
   "#{Rails.root}/public/assets"
 end