【PPSCI Export&Infer No.14】add export and inference function for deepcfd

[GoldenStain]

PR types

Others

PR changes

Others

Describe

为deepcfd案例添加了导出和推理功能

[HydrogenSulfate]

感谢提交PR，代码有几处修改建议，然后deepcfd的文档麻烦也补充一下模型导出和推理的命令，参考：

PaddleScience/docs/zh/examples/allen_cahn.md

Lines 24 to 40 in bddc575

	=== "模型导出命令"
	``` sh
	python allen_cahn_piratenet.py mode=export
	```
	=== "模型推理命令"
	``` sh
	# linux
	wget -nc https://paddle-org.bj.bcebos.com/paddlescience/datasets/AllenCahn/allen_cahn.mat -P ./dataset/
	# windows
	# curl https://paddle-org.bj.bcebos.com/paddlescience/datasets/AllenCahn/allen_cahn.mat --create-dirs -o ./dataset/allen_cahn.mat
	python allen_cahn_piratenet.py mode=infer
	```

[HydrogenSulfate]

LGTM

[HydrogenSulfate]

LGTM