If our users are to rely on the coder agent shutdown_script and graceful shutdown in general, we need to document how it behaves in different circumstances and what guarantees we provide.

Some initial thoughts on the matter:

• Should agent shutdown failure prevent de-provisioning?
• How long do we wait? Forever? Configuration options?
• What happens if an agent is disconnected and we can't initiate pre-provision shutdown request
  • Do we wait for X time before de-provision?
  • Do we wait indefinitely, but give users the option to shutdown anyway (with caveats of shutdown script may not be run, etc.)
• It's possible to coder start ws on an already started workspace, what should happen in this scenario?
  • Ideally, we would request the agent to shut down, but it may not be possible or may fail, what then?
• Should shutdown script run if startup script failed?
• Should startup script failure affect if we allow de-provisioning or not?

Related: #4677, #5914, #6139, #6175