POC: conditional creation of internal topics in Kafka Connect

[anton-liauchuk]

This is a small POC to demonstrate the possibility of disabling the creation of internal topics in Kafka Connect.
It might be useful in cases where internal topics contain information about a large number of connectors, and one or more of the original topics were accidentally removed or renamed in the configuration.

The new mode would provide the ability to:

• block the creation of internal topics.
• prevent Kafka Connect from starting if required topics are missing.

This way, there is a chance to troubleshoot the root cause instead of unexpected state of all connectors (for example, if the config topic is still present but the offset topic was accidentally removed or renamed, all the connectors will start from scratch).

Out of scope for this POC:

• no JIRA task yet — this PR is just to gather feedback.
• not fully implemented — there is a TODO item for the additional logic.
• the configuration name is not final — proposals are welcome.

[anton-liauchuk]

@C0urante, @mimaison, @chia7712 could you take a look at this POC?