Warn on Praefect LB timeout in docs
What does this MR do?
A potential gotcha with Praefect is that Gitaly RPCs from Sidekiq tasks are allowed to run for up to 6 hours, creating a risk that an overly aggressive LB timeout will kill the job.
Related issues
https://gitlab.com/gitlab-org/quality/gitlab-environment-toolkit/-/issues/290
These labels cause the MR to be added to code verification QA issues.