How do you programmatically include an entity type to a workflow? I have a workflow to which I want to include entity/content types programmatically since these content types will be included to the system by the installation of the module to which they reside. I'm not sure how to load the specific workflow object and attach the entity type to that via code.
You need the addEntityTypeAndBundle method from ContentModerationInterface 

A static way to implement it looks like:

$workflow = \Drupal::entityManager()-&gt;getStorage('workflow')-&gt;load([workflow_id]);

$workflow-&gt;getTypePlugin()-&gt;addEntityTypeAndBundle('node', 'article');

$workflow-&gt;save();