• Drop existing single page cdn integration from boot project.
• Create new spring-graphql-graphiql module containing graphiql integration.
• Makes graphiql optional which user can pull in as a dependency.
• spring-graphql-graphiql is a basic npm module which packages itself as
  a jar where boot autoconfig can integrate to.
• In a npm module graphiql itself is handled as a plain react app which allows
  some customisation like setting logo name to demonstrate how things are passed
  from boot properties into a react app itself.
• GraphiQlHandler's are changed to handle all traffic into /graphiql order to:
  • Handling main html in /graphiql/explorer
  • Redirect to /graphiql/explorer to get context path under /graphiql/
  • Handle main.js from classpath to get html to load it under /graphiql/
  • Handle config.js as a way to pass configuration options from server side
    and load those into react app. There are various long threads in GH and SO
    discussing this problem and I chose to load settings from a server side.
• Samples webmvc-http and webflux-websocket are changed to use this module.
  • webmvc-http is as it used to be.
  • webflux-websocket can now use subscription which gets first greeting instead
    of subscription request reply.
• Fixes Consider graphiQL integration #20
• Fixes GraphiQL setup to support websockets #131

Other notes:
This is a draft POC, so tests and more work to npm project would be added
later to polish things a bit.

If looking ok then this would give better foundation to think about
security and other things we'd like to have on this layer. Having a full
blown module and react code in typescript makes it easier to tweak things
instead of trying to rely on public stuff on cdn as a static app relying on
an internet access.

Both webmvc-http and webflux-websocket you can use:

query {
  greeting
}

With webflux-websocket when you use:

subscription {
  greetings
}

Where you get:

{
  "data": {
    "greetings": "Zdravo 007"
  }
}

Instead of:

{
  "data": {
    "upstreamPublisher": {
      "scanAvailable": true,
      "prefetch": -1
    }
  }
}