Change the default value of keep_runtime_alive from True to False

[tofarr]

Change the default value of keep_runtime_alive from True to False

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

---

This flag effectively stops any runtimes from being recycled by docker. Though some may want to do this, it is almost certainly not the preferred behavior for most use cases

---

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:eec904f-nikolaik   --name openhands-app-eec904f   docker.all-hands.dev/all-hands-ai/openhands:eec904f