#1650 RedisSinkCluster - Avoid recreating Counter

[justinweng-instaclustr]

This PR registers and stores the Counter instance in RedisSinkCluster instead of recreating the instance every time the method send_error_response is called.

Closes #1650

[codspeed-hq]

CodSpeed Performance Report

Merging #1658 will not alter performance

_{Comparing justinweng-instaclustr:1650-redissinkcluster-avoid-recreating-counter (c6688cd) with main (b129fae)}

Summary

✅ 37 untouched benchmarks

[rukai]

nice!

for the next reviewer:
The test introduced in this PR doesnt actually test the functionality that we are changing.
It tests RedisSinkSingle while this PR changes RedisSinkCluster.
This test was written as a simpler version of the the test we wanted to write against RedisSinkCluster.
However it was later found that we cant test RedisSinkCluster as its implementation of the shotover_failed_requests_count metric is incorrect in that it does not match the behaviour of all other shotover transforms that emit this metric.
This behavior was from before this PR, and fixing it is out of scope of this simple cleanup PR.
Since we discovered this after writing the test for RedisSinkSingle, we've kept that test around, since it at least tests some functionality.