Created by: chenwhql

PR types

Function optimization

PR changes

APIs

Describe

1. By advice of xiaoguang: https://github.com/PaddlePaddle/Paddle/pull/26718#discussion_r482674617, change jit.save/load configs to config
2. Rewrite all related example code based paddle 2.0 API

由于2.0-beta功能已经确定，里面使用的参数名仍然是configs，考虑到下一个版本参数改为config可能会引入不兼容问题，这里仍然兼容configs的写法

related FluidDoc PR：https://github.com/PaddlePaddle/FluidDoc/pull/2553