Don't try to database history topic if it exists already

Currently db history topic is created automatically.
Even if topic is in place, the `history.exists()` returns false unless there is some data in the topic.
This means, `initializeStorage` always executes topic creation when connector starts for the first time. In terms of security ACLs topic creation requires extra permissions on Cluster level, which is not desired in some environments.

https://docs.confluent.io/4.0.0/kafka/authorization.html#acl-format
https://kafka.apache.org/documentation/#operations_resources_and_protocols

So while topic could be already pre-created manually, `initializeStorage` may still fail (because of ACL rules) with the very confusing error:
>> Creation of database history topic failed, please create the topic manually

It would be good to have a config switch for auto-creation of database history topic