Support data sources containing cloud-optimized geotiffs

[favyen2]

Some data sources may point to stores of "Cloud-Optimized" GeoTIFFs that support range requests. Reads of arbitrary portions of these data sources are possible.

For these data sources, it would be ideal to avoid downloading the entire GeoTIFF. Instead, the user should be able to specify that only needed portions of the GeoTIFF should be read. However, this is different from our current ingestion process, where we read entire items; we could represent each block of the GeoTIFF as a different item, but this is far from ideal.

Changes:

• Implement a specialized tile store for cloud-optimized GeoTIFFs. The tile store says that the item is already present if it is present in the data source. The tile store reads and re-projects the data on the fly when requested.
• Adjust tile store API so that tile store is responsible for keeping track of the different projections. Currently, the projection is simply encoded in a layer, and the tile store is not actually aware of it.

[favyen2]

I think this needs more thought. The data source should be able to serve images directly to materialization rather than going through ingestion. Some data sources like ones serving WebMercator tiles might support materialization only, no ingestion.