FIX: Send TL2 promotion message to correct user (#21978)

Usually, when a user is promoted to TL2 two messages are sent. The
first one is a system message 'tl2_promotion_message' which triggers a
'system_message_sent' Discourse event.

When the event is fired and if Discourse Narrative Bot is enabled, then
a second message is sent to the recipient of the first message. The
recipients was determined by looking at the list of users that can
access that topic and pick the last one. This method does not work if
'site_contact_group_name' site setting is set because it adds the group
in the list of recipients.

A solution to this problem would have been to select the last user in
the list of 'topic_allowed_users', but an even better solution is to
pass the name of the recipients when the 'system_message_sent'
Discourse event is fired.

plugins/discourse-narrative-bot/plugin.rb

@@ -292,8 +292,7 @@ after_initialize do
     next if !SiteSetting.discourse_narrative_bot_enabled
     next if args[:message_type] != "tl2_promotion_message"
 
-    recipient = args[:post].topic.topic_users.where.not(user_id: args[:post].user_id).last&.user
-    recipient ||= Discourse.site_contact_user if args[:post].user == Discourse.site_contact_user
+    recipient = args[:recipient]
     next if recipient.nil?
 
     I18n.with_locale(recipient.effective_locale) do

plugins/discourse-narrative-bot/spec/discourse_narrative_bot/advanced_user_narrative_spec.rb

@@ -831,6 +831,7 @@ RSpec.describe DiscourseNarrativeBot::AdvancedUserNarrative do
         :system_message_sent,
         post: Post.last,
         message_type: "tl2_promotion_message",
+        recipient: recipient,
       )
     }.to change { Topic.count }
     expect(Topic.last.title).to eq(
@@ -849,6 +850,7 @@ RSpec.describe DiscourseNarrativeBot::AdvancedUserNarrative do
         :system_message_sent,
         post: Post.last,
         message_type: "tl2_promotion_message",
+        recipient: recipient,
       )
     }.to change { Topic.count }
     expect(Topic.last.title).to eq(
@@ -879,6 +881,7 @@ RSpec.describe DiscourseNarrativeBot::AdvancedUserNarrative do
         :system_message_sent,
         post: Post.last,
         message_type: "tl2_promotion_message",
+        recipient: recipient,
       )
     }.to change { Topic.count }
 
@@ -886,4 +889,17 @@ RSpec.describe DiscourseNarrativeBot::AdvancedUserNarrative do
     expect(topic.title).to eq("german title")
     expect(topic.first_post.raw).to eq("german body")
   end
+
+  it "invites the correct user when users in site_contact_group_name are invited to the system message" do
+    recipient = Fabricate(:user)
+    group = Fabricate(:group)
+    group.add(Fabricate(:user))
+    SiteSetting.site_contact_group_name = "#{group.name}"
+
+    SystemMessage.new(recipient).create("tl2_promotion_message", {})
+
+    expect(Topic.last.topic_users.map(&:user_id).sort).to eq(
+      [DiscourseNarrativeBot::Base.new.discobot_user.id, recipient.id],
+    )
+  end
 end