raise error when xarray dataset have wrong geo information

[vincentsarago]

another solution for #718 and #717

This is a bit more classic in a way that this PR adds checks for missing CRS or invalid Geographic bounds and then will raise an error directly when opening the dataset.

ref #725 (comment)

[j08lue]

IMO, the early failure here is nicer than the the configurable fallback CRS + potential head scratching of #725. 👌

[j08lue]

This gives users more helpful error messages when CRS is missing or their bounds are outside the expected range, closing

• Handle Xarray dataset without CRS #717
• XarrayReader considers tiles out of bounds when longitudes > 180? #718

I think this is preferable to the more auto-magic solution proposed in #725.

NB: I added a comment below to let the users know which range is expected, since this is a GDAL peculiarity - longitude values outside that range are perfectly fine elsewhere. Up to you whether you want to accept my suggestion.