Hi! Pystac is not using [the **preferred** media type for link of rel `item` which should be `application/geo+json` rather than `application/json`](https://github.com/radiantearth/stac-spec/blob/master/commons/links.md#hierarchical-relations): https://github.com/stac-utils/pystac/blob/2261b55ffbac6b52e6f56434bfd5508455dc3ac6/pystac/link.py#L478 Is there a reason for that? Thank you