[Omnibus] Allow configuring redis instance for trace chunks

What does this MR do?

This allows adding a setting redis_trace_chunks_instance and redis_trace_chunks_sentinels in gitlab.rb to create a new configuration file for a separate redis instance to store trace chunks.

Changelog: added

Related issues

This is part of gitlab-com/gl-infra/scalability#1094 (closed)

The new instance will added to GitLab-rails in gitlab!62767 (merged)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes in combination with: gitlab-com/gl-infra/scalability#1095 (closed) this new Redis instance would be accessible from GitLab-rails
• Documentation created/updated: The use of this extra Redis instance will be documented once we add the functionality in gitlab-com/gl-infra/scalability#1095 (closed)
• Tests added
• [-] Integration tests added to GitLab QA: This redis instance isn't used yet, but will be in: gitlab-com/gl-infra/scalability#1095 (closed) which will contain tests
• Equivalent MR/issue for the GitLab Chart opened: gitlab-org/charts/gitlab!2031 (merged)