Trace Chunks: Implement separate store in GitLab code base

Add the capability to distinctly configure a Redis instance to be used for chunk storage.

This will require:

1. A new redis-class Gitlab::Redis::TraceChunks, inheriting Gitlab::Redis::Wrapper like we have for SharedState,
2. Adding an instrumentation class to Gitlab::Instrumentation::Redis.

Status 2021-06-09

The implementation has been merged: Gitlab::Redis::TraceChunks is in gitlab-org/gitlab!63403 (merged). Waiting for it to be deployed.