Change logged-out WebUI HTML pages to be cached for a few seconds (#24708)

app/controllers/following_accounts_controller.rb

@@ -15,7 +15,7 @@ class FollowingAccountsController < ApplicationController
   def index
     respond_to do |format|
       format.html do
-        expires_in 0, public: true unless user_signed_in?
+        expires_in(15.seconds, public: true, stale_while_revalidate: 30.seconds, stale_if_error: 1.hour) unless user_signed_in?
       end
 
       format.json do