Enum value is not resolved correctly on buildFederatedSchema

Getting the following error when trying to build the federation schema using `buildFederatedSchema` - It seems that when defining default values for an input enum type property and the enum resolver has different values than keys, it doesn't recognize the default enum value: `Enum "TestEnum" cannot represent value: "A"`.

**Example:**

```
import { gql } from "apollo-server";

import { buildFederatedSchema } from "@apollo/federation";

const typeDefs = gql`
enum TestEnum {
A
}

input TestInput {
prop: TestEnum = A
}
`;

buildFederatedSchema({
typeDefs,
resolvers: {
TestEnum: {
A: "another_value_than_A",
},
},
});
```

**Packages:**

0.16.0 - @apollo/federation
2.13.1 - apollo-server
15.0.0 - graphql

Start by reproducing the reported failure through buildFederatedSchema with the provided TestEnum, TestInput, and resolver values. Trace how the federation schema handles the default enum value, then verify that the example builds successfully and that the existing enum behavior remains covered by tests.

Written by the indexing model from the issue text.