Natural Earth: Include version in URL

[kaedonkers]

Description

There are now five versions of Natural Earth features but currently the URL to download them in cartopy does not specify a version:
https://github.com/SciTools/cartopy/blob/main/lib/cartopy/io/shapereader.py#L323

The AWS S3 bucket that now hosts Natural Earth features supports version numbers:
nvkelso/natural-earth-vector#246 (comment)
but this has not been implemented in cartopy, which instead pulls the latest version available.

While this is not an issue in itself, adjusting the URL to optionally include the version of the Natural Earth feature will result in more reproducible behaviour.