Add honeypot fields and minimum fill-out time for sign-up form (#15276)

* Add honeypot fields to limit non-specialized spam

Add two honeypot fields: a fake website input and a fake password confirmation
one. The label/placeholder/aria-label tells not to fill them, and they are
hidden in CSS, so legitimate users should not fall into these.

This should cut down on some non-Mastodon-specific spambots.

* Require a 3 seconds delay before submitting the registration form

* Fix tests

* Move registration form time check to model validation

* Give people a chance to clear the honeypot fields

* Refactor honeypot translation strings

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

app/views/shared/_error_messages.html.haml

@@ -1,3 +1,6 @@
 - if object.errors.any?
   .flash-message.alert#error_explanation
     %strong= t('generic.validation_errors', count: object.errors.count)
+- object.errors[:base].each do |error|
+  .flash-message.alert
+    %strong= error