feat: implement third-party order sync

docs/migrations/202606040002_add_course_content.sql

@@ -0,0 +1,7 @@
+ALTER TABLE `courses`
+  ADD COLUMN `content` text NULL AFTER `name`;
+
+UPDATE `courses`
+SET `content` = JSON_UNQUOTE(JSON_EXTRACT(`raw_payload`, '$.content'))
+WHERE `content` IS NULL
+  AND JSON_EXTRACT(`raw_payload`, '$.content') IS NOT NULL;