v3 changes

[andrewiggins]

• Drop support for updating individual reports. All results must be reported at once using artifact flow
• Consider simplifying the pre/main stage setup. Perhaps pre stage does nothing for workflow_run and main will call reportTachRunning for workflow_run:requested and reportTachResults for workflow_run:completed?

The goal of the above changes is to dramatically simplify architecture and remove the need for comment locking since they remove the ability for multiple jobs to be modifying the comment at the same time