How to extend `node` resolver
Let's say I want to create my own (non-database backed) type. It's pretty straight forward with `makeExtendSchemaPlugin` to do something like this: 

```
      type RemoteUser implements Node {
        nodeId: ID!
        uname: String!
      }
```

And let's say for a user `alice`, I create the nodeId `base64Encode('["RemoteUser","alice"]')`

How would I extend the `node` resolver such that:

```
query MyQuery {
  node(nodeId: "WyJSZW1vdGVVc2VyIiwiYWxpY2UiXQ==") {
    nodeId
    ... on RemoteUser {
      uname
    }
  }
}
```

would actually work?
