Support WebSocket protocol

[bogeychan]

yoga({
  schema,
  graphiql: {
    subscriptionsProtocol: "WS", // this does nothing
  },
})

https://the-guild.dev/graphql/yoga-server/docs/features/subscriptions#graphql-over-websocket-protocol-via-graphql-ws

---

reported #12 (comment)

[kamalkech]

@bogeychan

"message": "Your subscription url is a websocket url, so your server must support graphql-ws or subscriptions-transport-ws protocol. If your server supports HTTP multipart subscriptions, change your subscription url to HTTP."
}