DEV: Convert min_trust_to_send_email_messages to groups (#24942)

We're changing the implementation of trust levels to use groups. Part of this is to have site settings that reference trust levels use groups instead. It converts the min_trust_to_send_email_messages site setting to send_email_messages_allowed_groups.

config/locales/server.en.yml

@@ -1979,6 +1979,7 @@ en:
 
     min_trust_to_send_messages: "DEPRECATED, use the 'personal message enabled groups' setting instead. The minimum trust level required to create new personal messages."
     min_trust_to_send_email_messages: "The minimum trust level required to send personal messages via email."
+    send_email_messages_allowed_groups: "Groups that are allowed to send personal messages via email."
     min_trust_to_flag_posts: "The minimum trust level required to flag posts"
     flag_post_allowed_groups: "Groups that are allowed to flag posts."
     min_trust_to_post_links: "The minimum trust level required to include links in posts"
@@ -2580,6 +2581,7 @@ en:
       ignore_allowed_groups: "min_trust_level_to_allow_ignore"
       self_wiki_allowed_groups: "min_trust_to_allow_self_wiki"
       create_tag_allowed_groups: "min_trust_to_create_tag"
+      send_email_messages_allowed_groups: "min_trust_to_send_email_messages"
 
     placeholder:
       discourse_connect_provider_secrets:

config/site_settings.yml

@@ -1727,6 +1727,13 @@ trust:
   min_trust_to_send_email_messages:
     default: "4"
     enum: "TrustLevelAndStaffSetting"
+    hidden: true
+  send_email_messages_allowed_groups:
+    default: "1|3|14"
+    type: group_list
+    allow_any: false
+    refresh: true
+    validator: "AtLeastOneGroupValidator"
   min_trust_to_flag_posts:
     default: 1
     enum: "TrustLevelSetting"