gitlab-managed-apps should be configurable as k8s namespace
### gitlab-managed-apps is now a fixed namespace
When the cluster-admin requirement is dropped, and the k8s integration can be done for specific namespaces also the `gitlab-managed-apps` should not be shared.
### Further details
It allows for further separations within a cluster, eg tiller restricted to the restricted namespaces for that team.
### Proposal
### What does success look like, and how can we measure that?
Have an option to specify an alternative for the `gitlab-managed-apps` namespace
### Links / references
issue