Refactor the service monitor to separate Gitlab Specific modules

By default, we deploy service monitors for the Gitlab applications. We could split the service monitors YAML file to separate the GitLab specific ones to a separate file and default to not deploying them.

There's a trade-off here about what should be the setting for the default. On one hand, not installing GitLab specific service monitors is less "surprising behaviour". In other words, the GitLab specific service monitors should be opt-in. On the other hand, this will have to be toggled in most clusters.