Introduces a new CI configuration option that allows
specifying the Kubernetes namespace that an environment
will be deployed to. This option does not currently
have any effect on deployments, deploying to the
specified namespace will be added as part of
https://gitlab.com/gitlab-org/gitlab/issues/27630

Example usage:

environment:
  name: production
  url: https://production.example.com
  kubernetes:
    namespace: production