Integrate graphiql into cynic-querygen-web

[obmarg]

It's functional right now, but would be good if we could write our queries in it, then click a button to write a query.

Reverse engineering functionality would also be great - like you give it rust structs and it spits out a query. Probably quite advanced though...

[obmarg]

Looks like it'd be relatively easy to just use code mirror instead of text areas and then pull in https://github.com/graphql/graphiql/tree/main/packages/codemirror-graphql (or possibly pull in the monaco version, though apparently that's still WIP)

[obmarg]

Could probably pair this with some UX improvements - ask the user for a schema first (either text area, file upload or point at a URL) then present the query editor.

[obmarg]

Most of this work is now done on the querygen-web-revamp branch. Left to do

• Finish the paste your schema flow.
• Handle the style of queries that graphiql explorer likes to build
• Get this building for netlify

[obmarg]

A first pass at this merged in #68

[obmarg]

#78 tracks all the remaining ideas I have for this, going to call this done & close.