FEATURE: mandatory fields for group site setting (#26612)

Automatically add `moderators` and `admins` auto groups to specific site settings.

In the new group-based permissions systems, we just want to check the user’s groups since it more accurately reflects reality

Affected settings:
- tag_topic_allowed_groups
- create_tag_allowed_groups
- send_email_messages_allowed_groups
- personal_message_enabled_groups
- here_mention_allowed_groups
- approve_unless_allowed_groups
- approve_new_topics_unless_allowed_groups
- skip_review_media_groups
- email_in_allowed_groups
- create_topic_allowed_groups
- edit_wiki_post_allowed_groups
- edit_post_allowed_groups
- self_wiki_allowed_groups
- flag_post_allowed_groups
- post_links_allowed_groups
- embedded_media_post_allowed_groups
- profile_background_allowed_groups
- user_card_background_allowed_groups
- invite_allowed_groups
- ignore_allowed_groups
- user_api_key_allowed_groups

spec/lib/site_setting_extension_spec.rb

@@ -857,6 +857,29 @@ RSpec.describe SiteSettingExtension do
     end
   end
 
+  describe "mandatory_values for group list settings" do
+    it "adds mandatory values" do
+      expect(SiteSetting.embedded_media_post_allowed_groups).to eq("1|2|10")
+
+      SiteSetting.embedded_media_post_allowed_groups = 14
+      expect(SiteSetting.embedded_media_post_allowed_groups).to eq("1|2|14")
+
+      SiteSetting.embedded_media_post_allowed_groups = ""
+      expect(SiteSetting.embedded_media_post_allowed_groups).to eq("1|2")
+
+      test_provider = SiteSetting.provider
+      SiteSetting.provider = SiteSettings::DbProvider.new(SiteSetting)
+      SiteSetting.embedded_media_post_allowed_groups = "13|14"
+      expect(SiteSetting.embedded_media_post_allowed_groups).to eq("1|2|13|14")
+      expect(SiteSetting.find_by(name: "embedded_media_post_allowed_groups").value).to eq(
+        "1|2|13|14",
+      )
+    ensure
+      SiteSetting.find_by(name: "embedded_media_post_allowed_groups").destroy
+      SiteSetting.provider = test_provider
+    end
+  end
+
   describe "_map extension for list settings" do
     it "handles splitting group_list settings" do
       SiteSetting.personal_message_enabled_groups = "1|2"