Proposing `xarray` upstream `entry-points`

[LecrisUT]

Having to use import pint_xarray is a bit clunky especially since it does not have explicit usage and can be deleted by some linters. How about proposing xarray upstream to expose a new entry-points to which pint-xarray can hook. They already have xarray.backends, but this feels like it doesn't fit there.

I am opening an issue here because I am not sure about the naming convention to propose, or how to give an example of how the hook should look like, e.g. at which stage should these entry-points be imported at.