Self-managed cluster > Don't create namespace when Auto DevOps is enabled automatically

Background

With https://gitlab.com/gitlab-org/gitlab-ce/issues/56557, we will allow users to choose whether or not they want to self-manage their clusters or have gitlab manage it for them. In a practical sense, this means create the namespace/service account.

Problem

If a user creates a cluster that they solely want to manage, and then we turn on Auto DevOps (ADO) automatically for their project, then it will create a namespace they didn't want.

Solution

For self-managed clusters, do not create a namespace for their cluster when Auto DevOps is turned on automatically for their project. Instead, fail the pipeline.