Support for `Node` interface-based federation.

[nmaquet]

Services implementing Relay's Global Object Identification Spec (i.e. the Node interface) should be allowed to be configured as boundary types without the need for an additional boundary accessor field.

[giautm]

Hey @nmaquet, I'm interested in this issue. So, is there any way to support/workaround for it?

[TheBeachMaster]

Hi, is there a proposed work-around for this? Anyone using ent will run into this issue.

[nmaquet]

@TheBeachMaster there no current plans to implement this but if someone is willing to give this a shot, I'd be happy to guide the efforts and assist with the PR.