chore: db 설정 환경변수로 수정

Author: 2jiyong

src/main/resources/application-dev.yml

@@ -1,8 +1,8 @@
 spring:
   datasource:
     url: jdbc:mysql://localhost:3306/intro
-    username: root
-    password: rhkrwogus1!
+    username: ${DB_USER}
+    password: ${DB_PASSWORD}
     driver-class-name: com.mysql.cj.jdbc.Driver
   jpa:
     show-sql: false