Using the `key` directive automatically defines types as extensions

[vinaybedre]

• [x] A short, but descriptive title. The title doesn't need "Apollo" in it.

• As soon an ObjectType is added a directed with key in it, apollo federation picks up as extensions and complains that there is no type definition for in any subgraph

• [X] When a published package is being used, the package management system Can be seen in repo shared below

• [X] The expected behavior. Federation should allow pickup those object types which are just defined with key directive and should not complain object definition is missing.

• [X] The actual behavior. Federation throws error as soon an object type is defined with key directive that that definition is missing.

• [X] A simple, runnable reproduction!

https://github.com/vinaybedre/federation-error

• [X] The federation version you are targeting.