feat: validate subgraph fetches

[lennyburdette]

This doesn't work yet because operation signatures aren't always valid documents.

[lennyburdette]

This is a false negative — the operation signature drops input fields.

storefrontGatewayCancellationSubmit a5eea3
==========================================
https://studio.apollographql.com/graph/xxx/operations?xxx&queryName=storefrontGatewayCancellationSubmit&variant=xxx

💣 Federation 1 supergraph query plan has subgraph fetch nodes that will fail
💣 Federation 2 supergraph query plan has subgraph fetch nodes that will fail
🎉 No difference in query plans

Subgraph fetch errors (Federation 1 supergraph)
-----------------------------------------------
* [service-eng-order-access-gql-federation] Field "CustomerOrderCancellationInput.orderProducts" of required type "[CancellationOrderProductInput!]!" was not provided.
    ```graphql
    mutation storefrontGatewayCancellationSubmit__service_eng_order_access_gql_federation__0 {
      requestCustomerOrderCancellation(customerOrderCancellation: {}) {
        __typename
        formattedRefundAmount
        orderProducts {
          __typename
          id
          status
        }
      }
    }
    ```
* [service-eng-order-access-gql-federation] Field "CustomerOrderCancellationInput.runId" of required type "ID!" was not provided.
    ```graphql
    mutation storefrontGatewayCancellationSubmit__service_eng_order_access_gql_federation__0 {
      requestCustomerOrderCancellation(customerOrderCancellation: {}) {
        __typename
        formattedRefundAmount
        orderProducts {
          __typename
          id
          status
        }
      }
    }
    ```

Subgraph fetch errors (Federation 2 supergraph)
-----------------------------------------------
* [service-eng-order-access-gql-federation] Field "CustomerOrderCancellationInput.orderProducts" of required type "[CancellationOrderProductInput!]!" was not provided.
    ```graphql
    mutation storefrontGatewayCancellationSubmit__service_eng_order_access_gql_federation__0 {
      requestCustomerOrderCancellation(customerOrderCancellation: {}) {
        __typename
        formattedRefundAmount
        orderProducts {
          __typename
          id
          status
        }
      }
    }
    ```
* [service-eng-order-access-gql-federation] Field "CustomerOrderCancellationInput.runId" of required type "ID!" was not provided.
    ```graphql
    mutation storefrontGatewayCancellationSubmit__service_eng_order_access_gql_federation__0 {
      requestCustomerOrderCancellation(customerOrderCancellation: {}) {
        __typename
        formattedRefundAmount
        orderProducts {
          __typename
          id
          status
        }
      }
    }
    ```