Update so we don't rebuild the domain used for output.gitlab_url

[bgood]

In main.tf local.domain is calculated using the var.domain and local.gitlab_address. However, in the outputs we rebuild the domain using local.gitlab_address. I think we should just use local.domain to build the output value for gitlab_url.

Because we rebuild the url using local.gitlab_address, the plan phase can produce this error:

Error: Invalid template interpolation value

  on .terraform/modules/gke-gitlab/outputs.tf line 23, in output "gitlab_url":
  23:   value       = "https://gitlab.${local.gitlab_address}.xip.io"
    |----------------
    | local.gitlab_address is null