Investigate Deployer for alternative artifact deployment

[lpeabody]

The artifact generator currently is silo'd into a Git-only push mechanism. It would be good to break this up and allow alternative deployment mediums such as what Deployer does. This seems similar to Capistrano which I used a long time ago, it was a very reliable method for self-hosted, non-Git-based deployments.

• Investigate Deployer capabilities (https://deployer.org/docs/8.x/recipe/drupal8#deploy)
• Abstract deployment process into a pluggable architecture
• Add Deployer deployment plugin