DEP: Drop Python 3.8 Support

[snowman2]

Related to #451

Community references:

• NEP-29 says numpy drops support for Python 3.8 in April 2023.
• pyproj
• rasterio
• geocube
• xarray

Note: This means rasterio pin will be moved to 1.2+ as wheels for Python 3.9 were not added to pypi until then ref.