Move Service templates topic on global nav

Moves Service templates topic to a more relevant place on the global nav (under Integrations).

• Before: https://docs.gitlab.com/ee/user/project/integrations/services_templates.html
• After: http://eread-move-service-templates-nav-item.178.62.207.141.nip.io/ee/user/project/integrations/services_templates.html

CC @deuley @arturoherrero