Features endpoint /collection/{c_id}/items has incorrect "self" link rel

[philvarner]

I see this on MSPC, so I assume it's a core bug.

In the response to:

https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-2-l2a/items

the Link with rel=self is https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-2-l2a instead of https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-2-l2a/items (missing the /items at the end)