Allow portfolio to book stories into sprints if any capacity is available

Currently, if Portfolio is attempting to schedule a story and a sprint already has work items booked and cannot fit the entire story, the story will attempt to be scheduled in the next available sprint that can fit the full estimate of the story. Portfolio will then split it into multiple sprints if it cannot fit into a full empty sprint.

As an admin, I believe it would be useful to allow Portfolio to book stories immediately, even if the next available sprint does not have the complete amount of capacity necessary to complete the story, and then split them into other sprints accordingly. Having an option to do this would also be useful.