bsdinstall scripted partition labeling

For unattended installation, bsdinstall(8) supports 'scriptedpart'
syntax to specify disk partitioning and mount points, but it doesn't
handle partition labels.

I'd like to define gpt partition labels for those partitions. It
looks as if there is underlying machinery in gpart_create() to
set labels, but at the moment it can only be done interactively.

Does anyone know if there was a specific reason for omitting
a label parameter for the unattended partition syntax (or just
"nobody's done the work yet") ?

I am thinking of making a PR to parse and pass label strings
for scripted installs - is there a reason not to?

Next up might be using label-based (i.e., "/dev/gpt/foo") in
the constructed fstab. I haven't looked at the fstab code in
bsdinstall - any gotchas to be aware of?