17403 implement collection specification

[``* `#17403` Implement collection specification``](https://community.openproject.org/work_packages/17403)
:+1: for sharing the specs

I would like to have the name improved. "collection" is very generic. "API" and "decorated" come to my mind. Especially, as this is shared with the whole set of specs (the namespace is not visible within a spec) this will otherwise get confusing.

Additionally, the difference between this shared examples and the shared "collection response" is confusing.