add explore function like in geopandas

[mhungen]

Geopandas provides a handy explore function that creates an interactive folium-map and displays the GeoDataFrame on it. This function is particularly useful when working with Jupyter notebooks.

Since I frequently work with rioxarray and geopandas, I developed a custom xarray accessor to add this functionality to xarray DataArrays as well. Given that rioxarray is the powerhouse handling the heavy lifting, this seems like a good fit for a new feature.

While my implementation is somewhat basic (DataArrays only), it is works and can be combined with the GeoDataFrame. If you're interested, I can create a PR for this feature.