fix MikroOrm .findOne returns stale/deleted data

[JoshuaOLoduca]

Content (작업 내용) 📝

1. Moved App initialization from constructor to an asynchronous private function.
2. Awaited db connection at appropriate time to fix issue (see below)

Screenshot for work content (작업 내용 스크린샷) 📸

Links (링크) 🔗

• Issue Links (이슈 링크) fixes #185

• API Links (API 스팩 문서)

• Development Links (개발 문서) Official Implementation of requestContext

• Document Links (기획 문서) mikro orm Identity map configuration

• Design Links (디자인 문서)

Etc (기타 사항) 🔖

Check List (체크 사항) ✅

• [ ] Issue (이슈)
• [ ] Tests (테스트)
• [ ] Ready to be merged (병합 준비 완료)
• [ ] Added myself to contributors table (기여자 추가)