Apollo v3 Subscriptions

**Describe the bug**

Since incorporating `graphql-modules` I've not been able to get a subscription socket to connect and stay connected. The socket sends a connection_init message and then dies.

I've not been able to find any examples or documentation on using this library with Apollo's latest subscription recommendations, which is to create a `SubscriptionServer` directly.

**To Reproduce**

Here's how I'm setting up the server. I'll try to find some time to create a sandbox for reproduction.

```
// applyDirectives visits directives in the schema and implements them
const schema = applyDirectives(schemaApplication.createSchemaForApollo());
const subscribe = schemaApplication.createSubscription();
const execute = schemaApplication.createExecution();

const app = express();

const httpServer = createServer(app);

const server = new ApolloServer({
schema,
context: createContext,
// allow introspection in non-prod environments
introspection: APP_ENV !== 'production',
plugins: [
{
async serverWillStart() {
return {
async drainServer() {
subscriptionServer.close();
},
};
},
},
ApolloServerPluginDrainHttpServer({ httpServer }),
],
});

const subscriptionServer = SubscriptionServer.create(
{
schema,
execute,
subscribe,
onConnect: (arg1: any) => {
console.log(`Connected`, arg1);
},
onDisconnect: (arg1: any) => {
console.log('Disconnected', arg1);
},
onOperation: (arg1: any) => {
console.log('Operation', arg1);
},
},
{
server: httpServer,
path: server.graphqlPath
},
);

await server.start();

server.applyMiddleware({
app,
});

httpServer.listen(PORT, () => {
console.log(
`🚀 Server ready at http://localhost:${PORT}${server.graphqlPath}`,
);
});
```

**Expected behavior**

I expect the Subscription client to connect via websocket and receive an ack, then maintain the connection.

I also expect the console logs to be invoked from my SubscriptionServer (they're not)

**Environment:**

- OS: MacOS 11.5.2
- `@graphql-modules/1.4.4`:
- NodeJS: 16.6.2

**Additional context**

The Apollo subscriptions example seems to use an API that's no longer part of their documentation in either v2 or v3.