Use metadata instead of properties on UserMessage. (spring-projects#3980)

Fixes spring-projects#3980

Auto-cherry-pick to 1.0.x

Signed-off-by: Mengqi Xu <[email protected]>

Author: remeio

spring-ai-model/src/main/java/org/springframework/ai/chat/messages/UserMessage.java

@@ -57,7 +57,7 @@ public UserMessage(Resource resource) {
 
 	@Override
 	public String toString() {
-		return "UserMessage{" + "content='" + getText() + '\'' + ", properties=" + this.metadata + ", messageType="
+		return "UserMessage{" + "content='" + getText() + '\'' + ", metadata=" + this.metadata + ", messageType="
 				+ this.messageType + '}';
 	}