This adds API docs for a new endpoint created to check the actions of a stack update without actually doing anything. Related Heat change: https://review.openstack.org/#/c/122473/ Co-Authored-By: Jason Dunsmore <jasondunsmore@gmail.com> Change-Id: I2ef30b9108a106045ec0ef1e380e47803659fda5 BP: update-dry-run