[BUG] kop upgrade may lead to offset loss

[aloyszhang]

Describe the bug
Currently, KoP starts with a configed partition number for offset topic

If we changed the offsetsTopicNumPartitions in broker.conf or upgrade from a lower version which does not have the configuratioin for offsetsTopicNumPartitions, kop can not find the correct partition for a given consumer group.

To Reproduce
Steps to reproduce the behavior:

1. start kop, create a topic , then produce some messages and consumer part of theses messages
2. change the offsetsTopicNumPartitions in broker.conf and restart
3. continue consume the same topic with the same consumer group
4. may see data loss

Expected behavior
kop should keep compatibility when upgrade or change the configuration