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>

config/locales/en.yml

@@ -751,6 +751,7 @@ en:
       functional: Your account is fully operational.
       pending: Your application is pending review by our staff. This may take some time. You will receive an e-mail if your application is approved.
       redirecting_to: Your account is inactive because it is currently redirecting to %{acct}.
+    too_fast: Form submitted too fast, try again.
     trouble_logging_in: Trouble logging in?
     use_security_key: Use security key
   authorize_follow:

config/locales/simple_form.en.yml

@@ -126,6 +126,7 @@ en:
         expires_in: Expire after
         fields: Profile metadata
         header: Header
+        honeypot: "%{label} (do not fill in)"
         inbox_url: URL of the relay inbox
         irreversible: Drop instead of hide
         locale: Interface language