v5 missing support for http batching

[kzlar]

Feature description

https://github.com/graphile/crystal/blob/main/grafast/grafserv/src/utils.ts#L298C27-L298C56
This check bails when an array of queries is sent to grafserv over http.

Motivating example

HTTP Batching is often used with Apollo client users to reduce the amount of http requests from the clients to the server. See https://www.apollographql.com/docs/react/api/link/apollo-link-batch-http
Postgraphile v4 did support this, so in a way not having this in v5 is a breaking change from v4 that is not documented.

Breaking changes

Shouldn't be any

Supporting development

I [tick all that apply]:

• am interested in building this feature myself
• am interested in collaborating on building this feature
• am willing to help testing this feature before it's released
• am willing to write a test-driven test suite for this feature (before it exists)
• am a Graphile sponsor ❤️
• have an active support or consultancy contract with Graphile