Rescale edge-aligner to enable registering images of different scales

[Yu-AnChen]

Add an optional --scale argument in the CLI to allow user specify relative resolution scales for each cycle. Current implementation only downscale images and add fixed filename prefixes when there are multiple scales.

[Yu-AnChen]

A couple of things we should probably discuss

1. Would use --cycle-pixel-sizes makes more sense than --scale in CLI?
2. Maybe should allow custom naming prefixes as compared to the fixed scaled_X.XX-filename.tif
3. The current implementation does not upscale images, so each output pyramid would have a different number of channels, I can see this becomes a problem if not handled properly in the computation workflow
4. Output only a specific scale is not implemented, it may be a useful feature to add