Add missing error for unsupported set-up configurations early

[phdum-a]

Higher order far-field boundary conditions are only supported in driven system, since like wave-ports they have a non LRC frequency dependance. Technically, this is enforced when building the matrices here:

palace/palace/models/farfieldboundaryoperator.cpp

Line 83 in 7804346

MFEM_VERIFY(farfield_bcs.Size() == 0 || order < 2 ||

It would be nice to enforce this along with all similar conditions in the config options. (e.g. we enforce no farfield be for the DC simulations in config).

PR is trivial, but would be nice for a second pair of eyes to double check logic / bool condition is correct.

[simlapointe]

LGTM. Tested it on my end and it works as expected; warning is displayed only when using absorbing bc with order=2.