feat: Add support for value types in federation (apollographql/apollo…

…-server#3063)

Value types are type definitions that live on multiple services (more specifically - types, inputs, interfaces, and unions). We've seen the desire internally and within the community to support the idea of a common type that multiple services can reference. A value type is identical by name, kind, and fields across all services.

In order to accomplish this, we've extended two of the existing validators: one for type names, and the other for field names. The changes to the validators permit duplicate type names and fields in the case that we've encountered a value type. The validators also provide some actionable, user-friendly errors in the case that we encounter a kind or field type mismatch.
Apollo-Orig-Commit-AS: apollographql/apollo-server@cca20d9

federation-js/package.json

@@ -16,7 +16,8 @@
   "dependencies": {
     "apollo-env": "^0.5.1",
     "apollo-graphql": "^0.3.3",
-    "apollo-server-env": "file:../apollo-server-env"
+    "apollo-server-env": "file:../apollo-server-env",
+    "lodash.xorby": "^4.7.0"
   },
   "peerDependencies": {
     "graphql": "^14.0.2"