Allow uneven horizontal partition for ConformalCubedSphereGrid

[navidcy]

At the moment, only even partitions are allowed.

Oceananigans.jl/src/MultiRegion/cubed_sphere_partitions.jl

Lines 21 to 23 in 2447ea7

	function CubedSpherePartition(; R = 1)
	# CubedSpherePartitions must have Rx = Ry
	Rx = Ry = R

When I implemented the cubed sphere partitioning, I thought that because of the cubed sphere opening that was the only allowed partitioning of the panels. But, e.g., the example below by @simone-silvestri showcases that this is not the case.