Make it easy to install and verify the installation of cert-manager

cert-manager can be installed using Helm or with regular Kubernetes manifests, but when using regular manifests it is difficult to customize the deployment. A kubectl cert-manager install command will make it easier for non-Helm users to customize the configuration of cert-manager, it will provide a way to see all the configuration options for a cert-manager deployment from the command line (i.e. by running kubectl cert-manager install --help). It will provide an option to wait for and verify the deployment, perhaps by integrating the code of cert-manager-verifier. And it may become the foundation of a future kubectl cert-manager upgrade command, which will help users safely upgrade and downgrade between cert-manager versions.