…kStage addApplication()

Currently there is no way of reordering stages/actions once they are created. Getting to

the Prepare and Execute change set actions while adding an application stage, we identified a

use case within our company that needs one or more intermediary sequential actions before

actually executing the change set. To resolve the problem, I suggest extending

the AddStageOptions interface with an optional property representing the number of

intermediary actions you need room for.

Closes aws#11333

…kStage addApplication()

naming changes as per reviewer recommendation

Closes aws#11333