Support region-writing (overwrite)

[tylanderson]

Region writing can be useful for initial large dataset creation or overwriting/updating a reference (new version etc)

I modified the geos-cf data pipeline to take an "overwrite" flag, which may be something to propagate down here

[sharkinsspatial]

@tylanderson I might be misunderstanding, but IIUC region writing is completely a function of how you define your processor. The virtualizarr-data-pipelines infrastructure makes no assumptions about how you write to your store (or if that store has already been expanded in a dimension to support writing)

[tylanderson]

@sharkinsspatial put up a rough example of what we could do in the protocol and example of implementing in the example processor