[FEATURE]: Anchoring should be applied separately to regions of non-contiguous mosaics

[thomaswilliamsastro]

Is your feature request related to a problem? Please describe.
Anchoring currently assumes that the mosaics are contiguous. This is mostly fine, but in some instances, the mosaic is split and some bits don't touch. There's no promise that the background correction is the same for each region (and in fact, clearly it isn't), so images should be segmented and anchoring solutions calculated separately for different regions

Describe the solution you'd like
Segment the image into discrete, contiguous regions, produce anchoring corrections for each region independently

Motivated by some of the NGC891 work @jchastenet has been working on