feat: upload backend api for testing uploader component

[Miles-hxy]

用于测试Uploader组件上传功能的服务端接口。
启动服务(上传的图片将保存在uploads文件夹)

cd v3/uploader-server
node index.js

组件使用demo:

import React, { useState } from 'react'
import { Uploader, Cell, FileItem, Space } from '@nutui/nutui-react'
import axios from 'axios'

const Demo1 = () => {
  const [list, setList] = useState<FileItem[]>([])

  async function upload(file: File) {
    const formData = new FormData()
    formData.append('file', file)

    const response = await axios.post(
      'http://localhost:3000/upload',
      formData,
      {
        headers: {
          'Content-Type': 'multipart/form-data',
        },
      }
    )
    console.log(response.data.url)
    return { url: response.data.url }
  }

  return (
    <>
      <Cell style={{ flexWrap: 'wrap' }}>
        <Space wrap>
          <Uploader
            uploadLabel="商品主图"
            value={list}
            onChange={setList}
            upload={(file: File) => upload(file)}
          />
          <Uploader upload={(file: File) => upload(file)} />
        </Space>
      </Cell>
    </>
  )
}
export default Demo1