docs: Update all examples to use esm modules

e.g.

'use strict'
const { createServer } = require('http')
const { Client } = require('undici')

const server = createServer((request, response) => {
  response.end('Hello, World!')
})

server.listen(() => {
  const client = new Client(`http://localhost:${server.address().port}`)

  client.request({
    path: '/',
    method: 'GET',
  }).then(({ body }) => {
    body.destroy()
  }).catch(error => {
    console.error(error) // should print an RequestAbortedError
    client.close()
    server.close()
  })
})

to

import { createServer } from 'http'
import { Client } from 'undici'
import { once } from 'events'

const server = createServer((request, response) => {
  response.end('Hello, World!')
})

await once(server, 'listening')

const client = new Client(`http://localhost:${server.address().port}`)

try {
  const { body } = await client.request({
    path: '/',
    method: 'GET',
  })
  body.destroy()
} catch (err) {
  console.error(error) // should print an RequestAbortedError
  client.close()
  server.close()
}

[hionnode]

Can I take it up?

[joaopedrocampos]

Hey @ronag! Do you think we could close this issue now since the PR is merged?