Programatically adding content - Core Media images

In trying to build a fully repeatable Drupal 8 site build, as well as wanting to include config, modules and themes, I want to be to insert content. This will allow boiler-plate or test content to be inserted, or will allow me to quickly build out a new version of my target site.  

In the first instance I was looking for a way to insert a image into a Core Media Image node.