Rename a computer, or set when it ends

Body: name, bot_mascot, and the end: ends_at (ISO 8601, in the future, at most 720 hours away), ends_in_hours (1 to 720), or ends_at null to keep it forever (send one of the two). When the end is up the computer is deleted: every end set or moved here deletes it, on a computer whose end was set before this rule (on_end "stop") too. on_end is not a choice: "delete" is accepted and changes nothing (alone, it needs a computer with an end: 400 INVALID_ENDS when there is none), and any other value ("stop" included) is 400 INVALID_ENDS. Changing the end needs write access to the workspace and clears a stopped computer’s ended mark. Only Linux and Windows computers can have an end. A running hourly computer prepays its run to the new end: a later end holds the extra (402 when the credit is short, an hour of the owner’s other hourly computers kept, nothing changed), an earlier one gives back what is past it, and ends_at null gives back what it has not used and bills it by the hour again. Only the workspace owner prepays a later end, and on a paid plan only signed in or with a key that has Billing write; anyone else who may write the workspace still moves the end, nothing more is held, the time past what is prepaid is billed by the hour, and the answer says prepay_warning. The answer carries prepaid_until, prepaid_cents and, when credit reached the balance, prepay_returned_cents: what reached it, which after a monthly credit refresh can be less than the unused part, or nothing.