Isolate Incident production health check
This removes the production health check handling from the overloaded
CheckProduction
task into its own dedicated class.
We split the execution path in the existing
auto_deploy:check_production
task based on the relevant environment
variable, but eventually these would all be dedicated CI jobs and Rake
tasks once the rest of the tasks are isolated.
I started with this one so that it's easier to implement a new rollback-ability check as part of gitlab-com/gl-infra/delivery#1718 (closed).
Related to gitlab-com/gl-infra/delivery#1748 (closed).