cannot import expressMiddleware from @apollo/server/src/express4
### Issue Description

I am trying to import expressMiddleware to set up graphql server with express; however, when starting my projecting I get an error... 

`Error: Package subpath './src/express4' is not defined by "exports" in /app/node_modules/@apollo/server/package.json`

My app.ts is the following...

```
import { expressMiddleware } from '@apollo/server/src/express4';
import { ApolloServer, ApolloServerOptions } from '@apollo/server';

export const useGraphQl = async (app: Express) => {
  // Graph QL route ('/graphql')
  const enableIntrospection = APOLLO_INTROSPECTION === 'true';

  const apollogConfig: ApolloServerOptions = {
    schema,
    context,
  };

  const server = new ApolloServer(apollogConfig);

  await server.start();
  app.use(expressMiddleware(server));
};
```

### Link to Reproduction

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### Reproduction Steps

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