provide a tool to convert HAR file to zerocode json/yaml teset case file

a user has to write a json/yaml file by hand to create a zerocode test case.
It will be much easier and more attractive to those who can not write codes if ZeroCode could proivde a har2case tool to conver HAR files created by Fiddler/Charles to ZeroCode test cases.
In this case, a user could work out testcases in such a play-and-record way and create test cases more effectively.

```
As a Developer or Test-Engineer //TODO - expand this
I want a har2case tool to do //TODO - expand this
- job 1 //TODO - expand this
- job 2 //TODO - expand this
- ...
So that I can(or do not have to) reuse the HAR files... //TODO - expand this
```

Start by reviewing the ZeroCode JSON/YAML test-case format and the HAR files produced by Fiddler and Charles. Define the supported HAR inputs, the generated test-case structure, and how the har2case tool should be invoked; done means a documented conversion workflow with representative coverage.

Written by the indexing model from the issue text.