Add requirements regarding "self" and "alternate" links for each collection

[heidivanparys]

As discussed in opengeospatial/ogcapi-features#410:

It is an oversight that we have not included anything about the self/alternate links for each Collection in the normative text. In the Collections resource there should be a self link for each Collection and in the Collection resource there should be self and alternate.

The resolution is:

Add these as recommendations with a note that clarifies that the missing links were an oversight and implementers should really implement the links.

I would suggest that we take these recommendations, turn them into requirements, and add those requirements to requirements class http://inspire.ec.europa.eu/id/spec/oapif-download/1.0/req/pre-defined in the INSPIRE good practice.

If/when a next version of OGC API - Features - Part 1: Core is published that changes the recommendations into requirements, we can remove them again from the INSPIRE good practice.

[heidivanparys]

GitHub-label "to be drafted"