[optimize] 分片上传建议限制 goroutine 数量，上传大文件时会占用大量内存

[LinkinStars]

	file, err := os.Open(u.LocalFilePath)
	if err != nil {
		return ret, err
	}
	defer file.Close()
	uploadRespChan := make(chan SuperFile2UploadResponse)
	for i := 0; i < sliceNum; i++ {
		buffer := make([]byte, sliceSize)
		n, err := file.Read(buffer[:])
		if err != nil && err != io.EOF {
			log.Println("file.Read failed, err:", err)
			return ret, err
		}
		if n == 0 {
			break
		}
                // 如果分片数量过多，这里会开大量 goroutine 进行上传，导致瞬间占用内存巨大
		go func(partSeq int, partByte []byte) {
			uploadResp, err := u.SuperFile2Upload(uploadID, partSeq, partByte)
			uploadRespChan <- uploadResp
			if err != nil {
				log.Printf("SuperFile2UploadFailed, partseq[%d] err[%v]", partSeq, err)
			}
		}(i, buffer[0:n])
	}

[jsyzchen]

在v0.0.7版本里已优化