You can use the migrate module with https://www.drupal.org/project/migrate_drupal_d8 to do that.
However, since you seem to be familiar with module development, I encourage you to try to see what you need that Contenta CMS has that you’d like in your project and add those parts manually.
Thanks for pasting this from Slack in here.
I added a not to clarify this in the main text: _When you need to upgrade Drupal and its modules, you do it just like with any other Drupal project. No need to upgrade Contenta CMS itself._
I hope that clarifies the question.
It is possible to do that in Contenta because Contenta CMS is Drupal after all. However that is something that your team will have to add to your project since Contenta does not ship with such tools out-of-the-box.