Add a warning if Sidekiq exporter and Sidekiq health checks are on the same port

What does this MR do?

This MR adds a warning for when Sidekiq exporter and Sidekiq health checks are running on the same port (and address). This is deprecated and will cause an error in release 15.0. This warning will help users so they know they have to update their settings.

We didn't add this to deprecations.rb because the config is not deprecated, but Sidekiq health checks is a newly added config, that now defaults to Sidekiq exporter (so releases < 15.0 don't crash)

Related issues

gitlab#347509 (closed)

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
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened