Serve lazy pyramid as virtual zarr file

[felixcremer]

This would enable that we expose a lazy computed Pyramid via the zarr interface to other visualisation packages that could then access only the part of the data that is needed and thereby only trigger the computations that are needed.

The result could then be visualised in the browser for example with this tool:
https://carbonplan.org/blog/maps-library-release

@meggart You said, you have some ideas regarding this implementation.