Add "sub deactivate" command

[llewelld]

Currently there's no obvious way to deactivate accounts that still have funds and haven't yet reached their expiration date. For users that request it, it would be helpful to provide a command to easilly deactivate an account (i.e. to bring the expiration date forward to today).

This could for example be in the form of an immediate deactivation command:

rcp-tab sub deactivate --subscription-id <id>

Another alternative might be to allow the expiration date of the subscription to be adjusted:

rcp-tab sub adjust --subscription-id <id> --date-to <date>

[Iain-S]

This sounds like a good QoL improvement. The more major change would be to allow approval expiry dates to be brought forward but the long-term goal would be to use the finance table in place of approvals so perhaps a short term fix would be better. The short-term fix would be to make rctab sub deactivate a shortcut to rctab approve --amount (-1 x remaining budget).