There is a new cool feature called Enroll contacts from list in Sitecore 9.1:
I'm wondering where the actual logic resists (which assembly and class). I'm going to utilize this functionality by defining a Sitecore task for this procedure.
Of course, I'm familiar with Sitecore documentation about Marketing Automation Operations API, but I would like to see the original solution here :) + maybe I can use some already existing method for that. So, I don't need to maintain my own code.