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

As part of https://github.com/coder/coder/issues/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).