Allow way to disable get requests for /graphql route in Apollo Server Express
By default, Apollo Server Express handles requests for get and post methods on the /graphql route. We would like get requests to /graphql to return a 404 and for the route to only be accessible via post. There does not seem to be a way to configure this at the moment. 

Right now I'm working around this by adding this to our Express server before we create the GQL middleware:

```
  app.use('/graphql', (req, res, next) => {
    if (req.method === 'POST') {
      next()
    } else {
      return res.sendStatus(404)
    }
  })
```