Ephemeral nodes… now more ephemeral!

Ephemeral nodes in Tailscale are designed for automated, short-lived workloads such as containers or CI/CD jobs, as they automatically remove themselves from the network once inactive. Previously, these nodes could clutter the network if their removal was delayed due to the coordination server's wait for potential reconnection. The introduction of the `tailscale logout` command now allows for immediate removal of these nodes, enhancing network cleanliness by quickly deleting nodes that will not return online. With Tailscale v1.30, nodes created through the CLI, which do not store state files, are instantly removed from the network upon shutdown. This improvement facilitates the reuse of MagicDNS names tied to defunct nodes and streamlines automation by allowing ephemeral nodes to be removed promptly through scripted deployments.