Refactor I/O utils; allow 'task' command line parameter in cli.py

[enyst]

End-user friendly description of the problem this fixes or functionality that this introduces

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below
  Add ability to use CLI with a task to execute automatically (the user doesn't need to enter in chat the first task).

---

Give a summary of what the PR does, explaining any non-trivial design decisions

This PR proposes:

• dedup CLI utils in their own openhands/io.py
• fix task argument in cli.py

---

Link of any specific issues this addresses
Fix #5719

---

To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:197a8b6-nikolaik   --name openhands-app-197a8b6   docker.all-hands.dev/all-hands-ai/openhands:197a8b6

[mamoodi]

@enyst just a gentle ping to check if this is still on going.

[enyst]

Sure, this is ready for re-review.