Use GraphiQL Workspace instead of plain GraphiQL

[mgwidmann]

Would much prefer this gem used the following project instead: https://github.com/OlegIlyenko/graphiql-workspace

Or at least a guide or something on how to do it...

[rmosolgo]

I'm going to take a look soon at integrating subscriptions with GraphiQL, so I'll follow up here if I add Workspace!