Construction of `SegmentedImage` from a labeled Image

[kimikage]

cf. https://discourse.julialang.org/t/how-to-convert-array-of-matrix-float64-to-segmentedimage-from-imagesegmentation-module/64418

I do not fully understand the use case of the OP in the above Discourse topic. However, I thought it would be nice to be able to save the segmentation result as a PNG or something, and resume work related to further segmentation from the saved image. Of course, it is possible to reconstruct SegmentedImage with fast_scanning, but the label values will change.