Add conditionals between two data cubes

[danlooo]

Allow to create a mask by comparing elements between two data cubes having the same dimensions:

cube["B01"] .> cube["B02"]

A simple merge_cube with overlap_resolver of process greater than (gt) does not work, because it is not supported e.g. by the backend https://openeocloud.vito.be/openeo/1.0.0

The python client adds the gt comparison to the process graph of reduce_dimension, circumventing merge_cube, because both bands originate from the same collection.

In addition, how to combine multiple conditionals e.g.

@. cube["B01"] > 1 && cube["B02"]  > 2

Need to implement &&, ||, xor, nor