DEV: use upload id to save in theme setting instead of URL. (#14341)

When we use URL instead it creates the problem while changing the CDN hostname.

db/migrate/20210914152002_update_value_on_theme_setting_for_upload_type.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+class UpdateValueOnThemeSettingForUploadType < ActiveRecord::Migration[6.1]
+  def up
+    execute <<~SQL
+      UPDATE theme_settings
+      SET value = (SELECT id FROM uploads WHERE uploads.url = theme_settings.value)
+      WHERE data_type = 6
+    SQL
+  end
+
+  def down
+    execute <<~SQL
+      UPDATE theme_settings
+      SET value = (SELECT url FROM uploads WHERE uploads.id = theme_settings.value)
+      WHERE data_type = 6
+    SQL
+  end
+end