Make the state transition confirmation form warning optional

The state transition confirmation form inherits the "This action cannot be undone." warning from its parent class, but this may not always be true. Some transitions can be "undone" if the workflow has defined bi-directional transitions and the developer knows there are no side effects based on that transition.

We can keep the default behavior of showing the warning, but perhaps we just add a "warning" option to the schema for transitions that defaults to true if not present and if present can be true or false.