Add support for showing warning if workspace startup script ran into an error

[mafredri]

As part of coder/coder#7757, we want to ensure the user knows if their workspace may be in an incomplete state.

• If startup script blocking behavior is enabled, we can query the coder API for agent lifecycle status and see if it is start_error, we can then show a warning popup
• If startup script behavior is non-blocking, we have two scenarios:
  1. If agent lifecycle has already entered start_error or ready we know whether or not to show the error
  2. If agent lifecycle is still starting or start_timeout, we can:
     1. Keep polling the status until it is known
     2. Never show the message (no work necessary)

We should at least implement i) and optionally ii.a).