fix: CloudWatch 메트릭 필터링 세분화로 비용 절감

- hikaricp/tomcat 전체 활성화 → 6개 필수 메트릭만 활성화
- HikariCP: connections.active, connections.idle, connections.pending
- Tomcat: threads.current, threads.busy, threads.config.max
- 예상 비용: $13.5/월 → $1.8/월 (약 87% 절감)

Author: Jinyshin

src/main/resources/application-staging.yml

@@ -78,5 +78,9 @@ management:
   metrics:
     enable:
       all: false
-      hikaricp: true
-      tomcat: true
+      hikaricp.connections.active: true
+      hikaricp.connections.idle: true
+      hikaricp.connections.pending: true
+      tomcat.threads.current: true
+      tomcat.threads.busy: true
+      tomcat.threads.config.max: true