add api GetBalance

[yzcyayaya]

新增 获取指定用户的账目信息。
https://docsv4.qingcloud.com/user_guide/development_docs/api/api_list/billing/get_balance/

issues:

package main

import (
	"fmt"
	"github.com/yunify/qingcloud-sdk-go/config"
	qc "github.com/yunify/qingcloud-sdk-go/service"
)

func main() {
	anotherConfiguration, _ := config.NewDefault()
	anotherConfiguration.AccessKeyID = "xxx"
	anotherConfiguration.SecretAccessKey = "xxx"
	qcService, _ := qc.Init(anotherConfiguration)
	balance, _ := qcService.GetBalance(&qc.GetBalanceInput{})
	fmt.Println(balance)
}