Change domain blocks to automatically support subdomains (#11138)

* Change domain blocks to automatically support subdomains

If a more authoritative domain is blocked (example.com), then the
same block will be applied to a subdomain (foo.example.com)

* Match subdomains of existing accounts when blocking/unblocking domains

* Improve code style

app/controllers/media_proxy_controller.rb

@@ -39,6 +39,6 @@ class MediaProxyController < ApplicationController
   end
 
   def reject_media?
-    DomainBlock.find_by(domain: @media_attachment.account.domain)&.reject_media?
+    DomainBlock.reject_media?(@media_attachment.account.domain)
   end
 end