More message types and examples for container-image artifacts
    
    Following up https://pagure.io/fedora-ci/messages/pull-request/18.
    
    The following new message types for the container-image artifact type
    are added:
    
    - container-image.test.queued
    - container-image.test.running
    - container-image.gate.queued
    - container-image.gate.running
    - container-image.gate.complete
    - container-image.gate.error
    
    Examples are also provided.