Add trademark warning to mastodon:setup task (#38548)

lib/tasks/mastodon.rake

@@ -27,6 +27,12 @@ namespace :mastodon do
         q.messages[:valid?] = 'Invalid domain. If you intend to use unicode characters, enter punycode here'
       end
 
+      if env['LOCAL_DOMAIN'].include?('mastodon') || env['LOCAL_DOMAIN'].include?('mstdn')
+        prompt.warn 'The Mastodon name is a trademark and its use is restricted.'
+        prompt.warn 'You can read the trademark policy at https://joinmastodon.org/trademark'
+        next prompt.warn 'Nothing saved. Bye!' if prompt.no?('Continue anyway?')
+      end
+
       prompt.say "\n"
 
       prompt.say('Single user mode disables registrations and redirects the landing page to your public profile.')