Update Redis::BufferedCounter to use its own instrumentation

What does this MR do and why?

This MR updates Redis::BufferedCounter to use its own instrumentation. Separating BufferedCounter from SharedState's storage label allows us to deprecate ClusterSharedState in the future.

Step 2 of gitlab-com/gl-infra/scalability#2651 (comment 1693732965)

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Before	After

How to set up and validate locally

1. On a gdk rails console, we see that the instrumentation_class is not overriden

[1] pry(main)> Gitlab::Redis::BufferedCounter.params
=> {:instrumentation_class=>Gitlab::Instrumentation::Redis::BufferedCounter, :path=>"/Users/sylvesterchin/work/gitlab-development-kit/redis/redis.socket", :db=>0}

2. On master branch, it is overriden

[1] pry(main)> Gitlab::Redis::BufferedCounter.params
=> {:instrumentation_class=>Gitlab::Instrumentation::Redis::SharedState, :path=>"/Users/sylvesterchin/work/gitlab-development-kit/redis/redis.socket", :db=>0}

MR acceptance checklist

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