Draft: Use destination_decision for Assignment request to prevent conflict
Assignments use destination to set Organisation, due to this, we switch to use destination_decision instead, as a way to link Assignment Request to the Person.
This allows use Assignment Requests to update Organisation's on projects that relies on it to set security.
Destination Decision is not used on Assignments, so it is future safe and will not conflict with future extensions of Assignment Requests and/or Assignments implementation.