feat: prevent clearing assigned topic partitions

[mhmcdonald]

Problem

This is a duplication of the work done in #648 fixing the issue described in #649

In order to use CooperativeStickyAssignor as the partition.assignment.strategy we need to adjust how the connector clears all the assigned topicPartitionWriters on close().

Solution

Does this solution apply anywhere else?

• yes
• no

If yes, where?

Test Strategy

Testing done:

• Unit tests
• Integration tests
• System tests
• Manual tests

Release Plan

[confluent-cla-assistant]

🎉 All Contributor License Agreements have been signed. Ready to merge.
✅ mhmcdonald
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