Namespace all federation directives

[jturkel]

There's probably some history here but it would be nice to have consistent namespacing of federation directives. Currently @inaccessible and @tag are not namespaced but all other federation directives are namespaced e.g. @key is exposed as @federation__key. apollo-federation-ruby could make the set of imported directives configurable but I'm not sure there's sufficient value in doing that vs. just namespacing everything to avoid conflicts with other directives. I'd be happy to put up a PR if you're open to this change.

[grxy]

This comment talks about why @inaccessible and @tag are imported vs namespaced.

[jturkel]

Ah! Makes sense.