Can not increase partitions in topic with only one partition

[poulhenriksen]

Describe the bug
A partitioned topic with only one partition can not be increased to have more partitions.

To Reproduce
Steps to reproduce the behavior:

1. Create a partitioned topic with one partition:

   bin/pulsar-admin persistent create-partitioned-topic \
   persistent://public/default/part_topic \
   --partitions 1
   

2. Try to increase the number of partitions:

   bin/pulsar-admin topics update-partitioned-topic persistent://public/default/part_topic -p 3
   

It then fails with:

13:57:59.057 [AsyncHttpClient-5-1] WARN  org.apache.pulsar.client.admin.internal.BaseResource - [http://localhost:8080/admin/v2/persistent/public/default/part_topic/partitions?updateLocalTopicOnly=false] Failed to perform http post request: javax.ws.rs.ClientErrorException: HTTP 409 Conflict
Topic is not partitioned topic

Reason: Topic is not partitioned topic

Expected behavior
It does not fail.

[sijie]

This has been fixed by #6560