New config default role

What this MR Does

1. Moves the code for our existing roles for postgres and redis into their own files in the config folder
2. Roles have been updated to only enable services, and not disable them. (If then needed to turn off a specific service that is fine, but it is no longer a role's job to disable all other services)
3. Adds an Application role that currently handles the old gitlab_rails enable field for compatibility, and can be used for configuring an application instance.
4. Set the default attributes to false for all our services, then add a DefaultRole that is enabled when no role is specified that turns them on. Maintaining our old functionality for users.

Fixes https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2615