fix(engine): iomapping for multi instance constructs

- execute input mappings such that local variables are created for every
  instance
- disallow output mappings as they require a larger refactoring of multi
  instance tasks (see CAM-2787) and have also questionable semantics
  because output mappings may override each other

related to CAM-2338
fix(engine): io mapping for events

- intermediate and end events
- throw parsing error for start and boundary events
- throw parsing error for event subprocesses

related to CAM-2400
fix(engine): propagate error that is thrown from event subprocess

- fixes ErrorPropagation and in particular the discovery of the execution
  responsible for executing boundary error events

related to CAM-2398
chore(engine-rest): change POST /task/{id}/comment to accept JSON

related to CAM-2402
fix(engine): fix infinite job creation caused by asyncAfter

related to CAM-2518