DEV: Convert email_in_min_trust to groups (#24515)

This change converts the `email_in_min_trust` site setting to
`email_in_allowed_groups`.

See: https://meta.discourse.org/t/283408

- Hides the old setting
- Adds the new site setting
- Add a deprecation warning
- Updates to use the new setting
- Adds a migration to fill in the new setting if the old setting was
  changed
- Adds an entry to the site_setting.keywords section
- Updates tests to account for the new change

After a couple of months we will remove the
`email_in_min_trust` setting entirely.

Internal ref: /t/115696

lib/email/receiver.rb

@@ -859,7 +859,8 @@ module Email
 
         user ||= stage_from_user
 
-        if !user.has_trust_level?(SiteSetting.email_in_min_trust) && !sent_to_mailinglist_mirror?
+        if user.groups.any? && !user.in_any_groups?(SiteSetting.email_in_allowed_groups_map) &&
+             !sent_to_mailinglist_mirror?
           raise InsufficientTrustLevelError
         end
 
@@ -1067,7 +1068,9 @@ module Email
         )
       elsif destination.is_a?(Category)
         return false if user.staged? && !destination.email_in_allow_strangers
-        return false if !user.has_trust_level?(SiteSetting.email_in_min_trust)
+        if user.groups.any? && !user.in_any_groups?(SiteSetting.email_in_allowed_groups_map)
+          return false
+        end
 
         topic_user = embedded_user&.call || user
         create_topic(