Add support for request batches

[jasonkuhrt]

Perceived Problem

• People want document batching apparently. Link round up:
  • https://github.com/jasonkuhrt/graphql-request/issues/517
  • ... (there are more, find them)

Ideas / Proposed Solution(s)

There are various features about this from various tools. I cannot find an actual spec though.

• https://www.apollographql.com/blog/batching-client-graphql-queries/
• https://medium.com/@dcdigital72/graphql-one-query-to-rule-them-all-batching-vs-merging-d216e6acb218
• https://www.apollographql.com/docs/router/executing-operations/query-batching/
• https://the-guild.dev/graphql/yoga-server/docs/features/request-batching

Ah, that last one does have a spec. That's great news as I don't have an interest in reading sporadic incomplete docs and blog posts to implement a feature in Graffle.

So, read this and report back next steps after understanding it: https://github.com/graphql/graphql-over-http/blob/main/rfcs/Batching.md

Something to keep in mind: Let's see if we can use the extension system to implement this feature. If not, why, and maybe we can enhance the extension system motivated by features needed to achieve this.

[jasonkuhrt]

This should be realized as an extension.