Graphql-playground: Ability to use graphql-ws instead of subscription-transport-ws

[Amareis]

This issue pertains to the following package(s):

• [ ] GraphQL Playground - Electron App
• [ ] GraphQL Playground HTML
• [X] GraphQL Playground
• [ ] GraphQL Playground Express Middleware
• [ ] GraphQL Playground Hapi Middleware
• [ ] GraphQL Playground Koa Middleware
• [ ] GraphQL Playground Lambda Middleware

subscription-transport-ws is (sort of) deprecated now: https://github.com/apollographql/subscriptions-transport-ws#graphql-ws
I think it's not really hard to implement grapqhl-ws support.

[Sytten]

The community has moved to graphql-ws now, I think it would better for playground to move too.

[brettjashford]

there's a PR to add this in graphql-playground-react https://github.com/graphql/graphql-playground/pull/1295