DEV: Hide message bus site settings (#15009)

Admins don't need to be changing these.

config/site_settings.yml

@@ -1863,26 +1863,33 @@ developer:
     hidden: true
     default: ""
   enable_long_polling:
+    hidden: true
     client: true
     default: true
   enable_chunked_encoding:
+    hidden: true
     client: true
     default: true
   long_polling_interval:
+    hidden: true
     default: 25000
     max: 25000
   long_polling_base_url:
+    hidden: true
     client: true
     default: "/"
   background_polling_interval:
+    hidden: true
     client: true
     default: 60000
     max: 99000
   polling_interval:
+    hidden: true
     client: true
     default: 3000
     max: 99000
   anon_polling_interval:
+    hidden: true
     client: true
     default: 30000
     max: 99000