Add a snap_to method to GeoBoxes to enable coercing GeoBoxes to the same pixel alignment

[robbibt]

I have two low-resolution GeoBoxes created by "zooming out" of two existing higher resolution dataset GeoBoxes:

lowres_geobox1 = ds1.odc.geobox.zoom_out(500)
lowres_geobox2 = ds2.odc.geobox.zoom_out(500)

Although these GeoBoxes share the same resolution and CRS, they do not share the same pixel alignment, resulting in pixels that do not align correctly:

I would like to be able to "snap" lowres_geobox2 to the pixel alignment of lowres_geobox1, so that both of my low resolution grids align perfectly:

Snapping is currently supported when creating a new GeoBox directly (e.g. via GeoBox.from_bbox), however it would be useful to have a GeoBox method that would allow a user to perform snapping on existing GeoBoxes as well.

[robbibt]

Unsnapped and snapped grids:

[Kirill888]

Probably also worth adding snap=False|True to zoom_out method, aligning two arbitrary geoboxes with compatible reprojections/resolution to each other is somewhat more involved (but not a lot more) than snapping to pixel size.

Maybe also worth supporting alignment between geoboxes of different resolutions when pixel sizes are related via exact integer scale 1x1 == 3x3.