cmd/rofl/machine: Rename terminate/cancel -> stop/remove

[matevz]

This PR renames:

1. oasis rofl machine terminate -> oasis rofl machine stop
2. oasis rofl machine cancel -> oasis rofl machine remove

It keeps old "terminate" and "cancel" subcommands as aliases.

Rationale

1. The "terminate" term may also associate with "terminate your subscription", which is not the case. The "stop" term is also more consistent with Docker's "start/stop/restart" terminology and also with oasis rofl machine restart.
2. The "cancel" term may be a bit too soft since it cancels your subscription and destroys the machine. I'd prefer to call this "remove" for consistency with other "add/remove" subcommands.

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