feature: clean up removed game server nodes

[lukepolo]

Replaces #471.

Removing a game server node only deletes its game_server_nodes row, so its Node, Jobs and volumes stay in the cluster. A new job runs every 5 minutes and cleans them up:

• Node: deleted once the node has no row and has been NotReady for 10 minutes. Control plane Nodes are never deleted.
• Jobs, claims and volumes: deleted once the node id has neither a row nor a Node. This covers the update, gamedata validation and game-streamer Jobs pinned to it. Match server Jobs are left alone, and files on the node's disk are kept.

A host that is still running re-creates its row on its next ping, so it is never cleaned up. Since the job runs on a schedule, it also cleans up nodes that were removed before this change.

Needs 5stackgg/5stack-panel#638 so the api can delete Nodes. Until then it logs a warning and keeps the Node, and with it the node's volumes.

A host that registers again after the cleanup gets its row and volumes back on its next ping, including the CS:GO volume.

Testing

Unit tests, plus two runs against a real k3s in Docker: the first deleted the removed Node and the leftovers of a node with no row and no Node, and the second deleted the volumes of the Node removed in the first run.