text: Title: [k8s] Add tini/other `init` for SkyPilot k8s pods
  Body: [tini](https://github.com/krallin/tini) or [dumb-init](https://github.com/Yelp/dumb-init) act as PID 1 to collect zombie processes and handle signals from k8s. We should add them to our docker images + k8s manifests when we launch SkyPilot pods. 