change WorkflowTransition#Builder to have contextPayload mandatory and also add to java doc how to obtain the contextPayload

End projects have to change methods like #obtainEditableInstance to #transition.

We need to provide more code guidance than currently with the org.hippoecm.repository.api.WorkflowTransition.Builder : At this moment, it is not clear what to do with contextPayload while some downstream projects might require it

Also deprecate all old methods like #obtainEditableInstance and document what to use instead