One-command onboarding of an interruptible GPU container (auth = an interruptible provisioning token via ?token=)

Returns a POSIX sh installer, run inside the container as curl -fsSL "<url>" | sh or wget -qO- "<url>" | sh. It downloads the interruptible agent for the container's architecture, verifies its sha256, and runs it; the agent enrolls the container as an interruptible node and detaches. Needs no root, systemd or capabilities. The token must be an interruptible one (orl provider provisioning-token create --class interruptible).