sketch XarrayTiler

[vincentsarago]

Add a XarrayTilerFactory to add tiling endpoints for zarr (xarray readable) dataset

This is mostly inspired from cogeotiff/rio-tiler#530 (comment)

TODO

• add test
• decide what happens for multiple dimension variable
• add the endpoints to the application

[vincentsarago]

This should create /zarr/tiles/... endpoints

Most of endpoints needs a URL (of a zarr dataset), a variable name (you can get the list of variable with /zarr/variables?url=...) and optionaly a time_slice={num of time slice} (will default to 0, the first one)

[vincentsarago]

Preview of the endpoints:

• /variables: return a list of available variables for a Zarr dataset
• /info: simple geo info about the dataset. I added show_times=True/False option if the users wants to get the time slices info (because the time dimension could be huge, I think it's safer to make it optional)