Clarifications for the Federation extension

[m-mohr]

Hm okay, indeed the schema does say it.

Then I think the text should be "In case not all back-ends of the federation support it, every discoverable resource [...] MUST list the back-ends that do support or host [it]." (bold to mark changes) Maybe even with the additional explanation "because otherwise clients will assume that all backends support or host it."

To be honest I would even prefer to rename the property to federation:only, in direct analogy to federation:missing, but I guess that would be too breaking? Both are lists of backends, but one gets the title federation:backends...

And as you mention the headings: Indeed they felt off to me when I first read the file. The 'restricting' nature of the term "supported only by" sounded like that section would be about cases where some things are missing, but the spec for federation:missing is actually the other section. Maybe "Lists of resources" should be extended to "Incomplete lists of resources" or "Lists of resources missing a subset of back-ends", as it's not really about how resources are listed, but how such a list is extended in case of problems.

Maybe this shouldn't be a comment here but a new issue in openeo-api.

Originally posted by @christophfriedrich in #101

[m-mohr]

There's no intent to change the naming of the properties we can just clarify the documentation.