Specify which dimensions are pyramided

[felixcremer]

Currently I am relaying on the types of the dimensions to check what are spatial dimensions to decide which are pyramided.
For that I am using the XDim and YDim types in DimensionalData.
When the zarr file on which I want to apply buildpyramids has spatial dimensions which are not named X or Y these are not recognized to be pyramided.
As a work around we can define the dimensions with the @dim macro but this should be made easier maybe with a keyword argument.

julia> @dim lat YDim "Latitude"

julia> @dim lon XDim "Longitude"

[felixcremer]

This was closed in #76