feat: prevent clearing assigned topic partitions

[mhmcdonald]

Problem

This is a duplication of the work done in https://github.com/confluentinc/kafka-connect-storage-cloud/pull/648 fixing the issue described in https://github.com/confluentinc/kafka-connect-storage-cloud/issues/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
• [x] no

If yes, where?

Test Strategy

Testing done:

• [ ] Unit tests
• [ ] Integration tests
• [ ] System tests
• [ ] Manual tests

Release Plan

[confluent-cla-assistant[bot]]

:tada: All Contributor License Agreements have been signed. Ready to merge.
:white_check_mark: mhmcdonald
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