FEATURE: Add creator and logging for CustomEmoji (#28004)

* FEATURE: Add logging for CustomEmoji

We didn't provide any logs for CustomEmoji before, nor did we record the
person who added any emoji in the database. As a result, the staff had
no way to trace back who added a certain emoji.

This commit adds a new column `user_id` to `custom_emojis` to record the
creator of an emoji. At the same time, a log is added for staff logs to
record who added or deleted a custom emoji.

app/controllers/admin/emojis_controller.rb

@@ -28,9 +28,12 @@ class Admin::EmojisController < Admin::AdminController
 
       data =
         if upload.persisted?
-          custom_emoji = CustomEmoji.new(name: name, upload: upload, group: group)
+          custom_emoji =
+            CustomEmoji.new(name: name, upload: upload, group: group, user: current_user)
 
           if custom_emoji.save
+            StaffActionLogger.new(current_user).log_custom_emoji_create(name, group: group)
+
             Emoji.clear_cache
             { name: custom_emoji.name, url: custom_emoji.upload.url, group: group }
           else
@@ -50,7 +53,12 @@ class Admin::EmojisController < Admin::AdminController
     name = params.require(:id)
 
     # NOTE: the upload will automatically be removed by the 'clean_up_uploads' job
-    CustomEmoji.find_by(name: name)&.destroy!
+    emoji = CustomEmoji.find_by(name: name)
+
+    if emoji.present?
+      StaffActionLogger.new(current_user).log_custom_emoji_destroy(name)
+      emoji.destroy!
+    end
 
     Emoji.clear_cache