Socket: 🔧 The server sends a success message after a chat message is saved successfully

[psychology50]

작업 이유

• We improved error messages in Ignore: ✏️ Add Send Message Headers to the Error Message #212, but the client still can't handle success messages.
• Therefore, we need to send a message to notify the client when their chat message is successfully processed.

작업 사항

• The server sends a message that includes x-message-id to success queue after the chat message is successfully published.

리뷰어가 중점적으로 확인해야 하는 부분

• Since I am not very experienced with Kotlin, please review the code style.

발견한 이슈

• When the client tries to subscribe, if the receipt header is missing, the server throws an error. 😅