Limit edit status option for confirmed purchase order

[jmcameron]

When editing the status of a purchase order, if the purchase order is confirmed, the edit dialog should not show the "Waiting Confirmation" status if it is already confirmed.

If you select this option and click [Submit] it will fail (The red error message says "You are not allowed to perform this operation".

Either it should be possible to change the status to "Waiting Confirmation" or this option should not be shown.

[jniles]

See https://github.com/third-culture-software/bhima/issues/4789 for a proposed solution. And https://github.com/third-culture-software/bhima/issues/5672 for other discussion.