TEST - handle task artifacts - task executer Integration Tests

[jackschofield23]

Integration Tests for #129

• Sending artifacts on TaskDispatchEvents.
• TaskUpdateEvent includes relative path

[RemakingEden]

Int tests:

• Send task dispatch message with artefact
• Receive task update event with same artefact

Data:

• Correct artefact (Happy path)
• Null

[RemakingEden]

Test matrix https://docs.google.com/spreadsheets/d/1ohYtCKHc5911SDSH0gJDCDrotRVnk2KmgcCsxYAPK0U/edit

[JoeBatt1989]

All TaskDispatch and TaskCallback events used in test include Inputs and Outputs respectively. Moving to done