Allow admins to configure rack-timeout for Puma
Problem to solve
On self-managed GitLab instances using Unicorn, admins sometimes find it necessary to increase the unicorn worker timeout in order get a particularly slow page to load. However, with Puma we have a hard-coded timeout of 60 seconds, leaving admins with no workaround when GitLab performs poorly.
User experience goal
Slow-loading pages are still accessible when using Puma.
Make rack-timeout configurable.