Move rack_attack section of gitlab.yml to a template for rails based containers

Broken out from #847 (closed), improving DRY patterns

Move the rack_attack section of gitlab.yml to a template, and have all rails based containers pull this into their ConfigMaps.

This appears to only be needed by Unicorn, and has chart-local configuration items. These items either need moved to global, or this section can be kept out of the other rails charts.