[RFC] Procedure call batching

[KATT]

Would be cool if one could automatically batch all parallel queries into the same request on the client. https://github.com/graphql/dataloader for inspo.

Shouldn't be that hard to do. Could enable some cool stuff like making a db transaction across multiple parallel mutations.

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considerations:

• should query/mutation/subscriptions be able to batched together or should we batch per type?
• query-specific: how to avoid caching of a mix of "public"/"private" procedures if one uses caching
• subscriptions: tricky
• opt-in or opt-out?

[KATT]

Might need to happen after #412

[KATT]

Solved by #461