feat: add batching support with batchRequests

[GeoffreyHervet]

Add a new function to support GraphQL batching
closes #13
closes #75

---

import { batchRequests } from '../src'
;(async function () {
  const endpoint = 'https://api.spacex.land/graphql/'

  const query1 = /* GraphQL */ `
    query ($id: ID!) {
      capsule(id: $id) {
        id
        landings
      }
    }
  `
  const variables1 = {
    id: 'C105',
  }

  interface TData1 {
    data: { capsule: { id: string; landings: number } }
  }

  const query2 = /* GraphQL */ `
    {
      rockets(limit: 10) {
        active
      }
    }
  `

  interface TData2 {
    data: { rockets: { active: boolean }[] }
  }

  const query3 = /* GraphQL */ `
    query ($id: ID!) {
      core(id: $id) {
        id
        block
        original_launch
      }
    }
  `

  const variables3 = {
    id: 'B1015',
  }

  interface TData3 {
    data: { core: { id: string; block: number; original_launch: string } }
  }

  const data = await batchRequests<[TData1, TData2, TData3]>(endpoint, [
    { document: query1, variables: variables1 },
    { document: query2 },
    { document: query3, variables: variables3 },
  ])
  console.log(data[0].data.capsule)
  console.log(data[1].data.rockets)
  console.log(data[2].data.core)
  // console.log(JSON.stringify(data, undefined, 2))
})().catch((error) => console.error(error))

[jasonkuhrt]

Could you try adding a test or two

[sswayney]

If this PR could be merged I would be very happy. This feature is all that is missing to give me the go-ahead to use this lib for my project. @GeoffreyHervet is there anything you need?

[GeoffreyHervet]

@sswayney Thanks, I just had to add tests as suggested @jasonkuhrt

[jasonkuhrt]

LGTM

[jasonkuhrt]

@GeoffreyHervet Ah, one thing, docs in REDAME would be great thanks!

[GeoffreyHervet]

@jasonkuhrt I'll add it !