[Issue 1105][pulsaradmin] fix AutoTopicCreation for type non-partitioned (#1107)

Fixes #1105

### Motivation

To allow setting the AutoTopicCreation policy to non-partitioned it is required to not send the partitions parameter, by making Partitions a pointer instead of an int this is possible.

### Modifications

Change the type of Partitions in TopicAutoCreationConfig from int to *int

Author: Tom Jorissen

pulsaradmin/pkg/utils/topic_auto_creation_config.go

@@ -20,5 +20,5 @@ package utils
 type TopicAutoCreationConfig struct {
 	Allow      bool      `json:"allowAutoTopicCreation"`
 	Type       TopicType `json:"topicType"`
-	Partitions int       `json:"defaultNumPartitions"`
+	Partitions *int      `json:"defaultNumPartitions"`
 }