graphql: add support for subscriptions

[kolharsam]

• add a websocket server that will work alongside the HTTP server
• the server should support the graphql-ws sub-protocol for communication with clients
  • graphql-ws - TS Server implementation https://github.com/enisdenjo/graphql-ws/blob/master/src/server.ts
• extend the same support for query's to subscriptions

[kolharsam]

https://agmprojects.com/blog/building-a-rest-and-web-socket-api-with-actix.html

[kolharsam]

Note to self: to check these out

• https://wundergraph.com/blog/deprecate_graphql_subscriptions_over_websockets
• https://stackoverflow.com/questions/28582935/does-http-2-make-websockets-obsolete