added missing setter for metadata

spring-boot-admin-starter-client/src/main/java/de/codecentric/boot/admin/client/config/AdminClientProperties.java

@@ -100,4 +100,8 @@ public class AdminClientProperties {
 	public Map<String, String> getMetadata() {
 		return metadata;
 	}
+
+	public void setMetadata(Map<String, String> metadata) {
+		this.metadata = metadata;
+	}
 }