Change NUOPC default to unmappedAction=error

[danrosen25]

The initial release of NUOPC set the default connector unmappedAction to ignore. In the next major release (9.0.0) we should change the default connector unmappedAction to error. Users should be aware of situations where regridding is incomplete. The simple solution is for users to set an extrapolation method that will map any previously unmapped cells. The more advanced solution is to intentionally ignore unmapped cells and handle them in user code (this can be done with fill values and zeroRegion select).

[anntsay]

If change the default -> it would not be backward compatible.. and it is an interface change. it would have to be a major release in 9.0.0.

caution: this may break NUOPC app prototypes.

will plan to give community heads up.