Add meachanism to save a TileArray to disk e.g. zarr

[danlooo]

Datasets in YAXArrays don't support to be saved if they are bigger than memory, even if it's just a skeleton.

julia> save_dggs_dataset("test.zarr", dggs_ds)
ERROR: UndefVarError: `Zarr` not defined in `DGGS`
Suggestion: check for spelling errors or missing imports.
Hint: a global variable of this name also exists in Zarr.
Stacktrace:
 [1] _save_dggs_dataset_zarr_direct(file_path::String, ds::DGGSDataset{…}, chunks::@NamedTuple{…}; kwargs::@Kwargs{})
   @ DGGS /Net/Groups/BGI/people/dloos/prj/dggs-prj/DGGS.jl/src/datasets.jl:130
 [2] _save_dggs_dataset_zarr_direct(file_path::String, ds::DGGSDataset{…}, chunks::@NamedTuple{…})
   @ DGGS /Net/Groups/BGI/people/dloos/prj/dggs-prj/DGGS.jl/src/datasets.jl:128
 [3] save_dggs_dataset(file_path::String, ds::DGGSDataset{…}; chunks::@NamedTuple{…}, kwargs::@Kwargs{})
   @ DGGS /Net/Groups/BGI/people/dloos/prj/dggs-prj/DGGS.jl/src/datasets.jl:115
 [4] save_dggs_dataset(file_path::String, ds::DGGSDataset{…})
   @ DGGS /Net/Groups/BGI/people/dloos/prj/dggs-prj/DGGS.jl/src/datasets.jl:110
 [5] top-level scope
   @ REPL[19]:1
Some type information was truncated. Use `show(err)` to see complete types.