Implement the op PrepVasp

[wanghan-iapcm]

This op prepare the VASP DFT calculation tasks. This op takes the vasp input template and a list of configurations, outputs a list of path that contains all the necessary files to run a VASP DFT task.

We have to implement the execute method of the class. What the op does is explained in the docstr of the class and the interface of the execute method is provided in the docstr of the method.

One can also take the implementation of PrepDPTrain as an example for the PrepVasp