Consider making the `query` parameter optional?

Reference:
https://github.com/graphql/graphql-over-http/pull/175#discussion_r917932366

just pulling this out in case there is not another issue to track

in my view, query should be optional so that persisted operations, automatic or otherwise, could be considered spec-compliant.

The spec language would say something like that “the document to be executed, when sent within the http request, should be contained within the optional query parameter. When not included, the implementation can use an implementation defined method of determining the operation…”

otherwise, spec compliant implementations might be tempted to send empty query parameters to be compliant. See: https://github.com/dotansimha/graphql-yoga/pull/1589#discussion_r944641768

Tagging below discussants from those issues:
@enisdenjo
@ardatan
@glasser
@benjie