Artifact Types List Endpoint

[jacksonoberkirch]

What I'm doing:

Updating client with get and adding artifact type module needed for artifact types list endpoint What it looks like:

## Returns
  {:ok, %{status: "ok", response: %{ "artifact_types": [
            {
                "slug": "story",
                "name": "Story",
                "description": "This is a story"
            }
  ]}}}
  """
  def list_artifact_types(config) do
    ArtifactType.list(config)
  end

What I'd like feedback on:

Anything you can think of, let me know if you have any questions!