Remove the line break hack when using Server Sent Events (SSE)

[arey]

The Pull Request #3 introduces a hack for fixing The line break problem when using Server Sent Events (SSE)

• Hack on server side: https://github.com/spring-petclinic/spring-petclinic-langchain4j/blob/v3.3.3/src/main/java/org/springframework/samples/petclinic/chat/AssistantController.java#L54
• hack on client side: https://github.com/spring-petclinic/spring-petclinic-langchain4j/blob/v3.3.3/src/main/resources/static/resources/js/chat.js#L101

This issue involves finding a better approach than substituting line breaks \n in <br>.