Playground feature parity

This is a follow up from https://github.com/graphql/graphql-wg/issues/1648. The current situation of having 2 different IDEs is confusing. Playground hasn't had much activity lately and it'd be grand to consolidate everything in GraphiQL.

That being said, as a Playground user, there are several aspects that I like better there and I'm curious what the team thoughts are about them.

The full context is in https://github.com/graphql/graphql-wg/issues/1648 but the most important ones are:

* [ ] Copy as curl
* [ ] SDL/JSON download
* [ ] Editable endpoint url
* [ ] Multi column schema doc
* [ ] Search the docs
* [ ] Maybe schema polling? (I would have expected this to be available but didn't find it)
* [ ] Settings editor

This is all from a cursory look of comparing the sample index.html ([playground](https://github.com/graphql/graphql-playground/blob/main/packages/graphql-playground-html/minimal.html), [graphiql](https://github.com/graphql/graphiql/blob/main/examples/graphiql-cdn/index.html)). It may very well be that GraphiQL has all those features but that they require more configuration, it which case, some better defaults would be very welcome.

Any thoughts?