KafkaSinkCluster: route *PartitionReassignments

[rukai]

This PR adds support for both ListPartitionReassignments and AlterPartitionReassignments.
They are done together because having both makes it easier to write a useful test.
The test looks like:

1. Create a partition reassignment by calling admin.alterPartitionReassignments
2. List partition reassignments by calling admin.listPartitionReassignments and then asserting that the created reassignment is listed.

The actual handling of the message types is trivial to implement and just requires routing to a random node.

[codspeed-hq]

CodSpeed Performance Report

Merging #1811 will not alter performance

_{Comparing rukai:list_partition_reassignments (d120531) with main (bab7b97)}

Summary

✅ 38 untouched benchmarks