[탁우현] Announcement Entity API 생성

[WooHyunTak]

구현할 기능

Announcement 도메인 API 생성

세부 작업 목록

• GET /
• GET /:announcementId
• POST /
• POST /:announcementId/pin
• PATCH /:announcementId
• DELETE /:announcementId
• DELETE /:announcementId/pin

참고 사항