Queryables link missing

[m-mohr]

Describe the bug

The queryables link is missing from the root endpoint, and it seems also from individual collections.
It has been there before (with a wrong rel type, but anyway).

Expected behavior
Add links with relation type http://www.opengis.net/def/rel/ogc/1.0/queryables again to the root endpoint and the individual collections.

[m-mohr]

Maybe related to stac-utils/stac-fastapi#401

[m-mohr]

It also looks like the filters don't work for the items endpoints:
https://planetarycomputer.microsoft.com/api/stac/v1/collections/sentinel-5p-l2-netcdf/items?filter-lang=cql2-text&filter=s5p:product_name%20=%20%27ch4%27

Makes it pretty hard to find specific data in some collections, e.g. S5P.

Related PR: stac-utils/stac-fastapi-pgstac#89