MINOR: Change topic-exists log for CreateTopics from INFO to DEBUG (#7666)

Reviewers: Ismael Juma <ismael@juma.me.uk>

core/src/main/scala/kafka/server/AdminManager.scala

@@ -179,6 +179,9 @@ class AdminManager(val config: KafkaConfig,
         CreatePartitionsMetadata(topic.name, assignments, ApiError.NONE)
       } catch {
         // Log client errors at a lower level than unexpected exceptions
+        case e: TopicExistsException =>
+          debug(s"Topic creation failed since topic '${topic.name}' already exists.", e)
+          CreatePartitionsMetadata(topic.name, Map(), ApiError.fromThrowable(e))
         case e: ApiException =>
           info(s"Error processing create topic request $topic", e)
           CreatePartitionsMetadata(topic.name, Map(), ApiError.fromThrowable(e))