allow users to specify a license

[sbillinge]

ideally give a list of possibilities so that they don't have to remember correct syntax then have them pick.

[sbillinge]

Not sure if this is worth it as we are kind of settling on BSD-3 clause. Maybe better to change Regolith license to BSD-3 than do this.... Let's hold off on this one.

[bobleesj]

also push off to the next release? BSD-3 seems sufficient for now and we could consider this both in skpkg when we have some demand for this featrue?