fix: 백엔드 배포환경 url 수정

Author: seungwookc97

src/main/resources/application.yml

@@ -68,7 +68,7 @@ custom:
   prod:
     cookieDomain: ${BASE_URL}
     frontUrl: "https://www.${custom.prod.cookieDomain}"
-    backUrl: "https://${custom.prod.cookieDomain}"
+    backUrl: "https://api.${custom.prod.cookieDomain}"
   site:
     cookieDomain: "${custom.dev.cookieDomain}"
     frontUrl: "${custom.dev.frontUrl}"