Add support for promotion of docker images

[rasheedamir]

Multiple clusters is a common practice. A non-production and production cluster is very common. In a continuous integration pipeline, we want to achieve promotion to all environments and clusters. We need a way to promote images from cluster to cluster.

First thoroughly read following:

• https://github.com/openshift/jenkins-client-plugin#moving-images-cluster-to-cluster
• https://docs.okd.io/latest/dev_guide/managing_images.html#managing-images-mirror-registry-images

e.g.

stage('Move Image') {
	steps {
    	withDockerRegistry([credentialsId: "source-credentials", url: "source-registry-url"]) {

        	withDockerRegistry([credentialsId: "destination-credentials", url: "destination-registry-url"]) {

            	sh """
                	oc image mirror mysourceregistry.com/myimage:latest mydestinationegistry.com/myimage:latest
              	"""

            }
         }
     }
}