fix: cannot import sub-collection of postman

[SamYSF]

Fixes #101

What this PR does / why we need it:
1.The original logic cannot convert sub folders beyond one Postman folder.
2.I can only convert the body in JSON format is raw.Therefore,I have modified the structure of the PostmanBody according to the document https://learning.postman.com/collection-format/advanced-concepts/request-definition/. Now, I need to convert it to test suite. Do I need to modify the code structure of test suite Request?

type RequestBody struct {
	Value  string `json:"value" yaml:"value"`
	isJson bool
}

[CLAassistant]

All committers have signed the CLA.

[sonarcloud]

Quality Gate failed

Failed conditions
7.9% Duplication on New Code (required ≤ 3%)

See analysis details on SonarCloud

[LinuxSuRen]

Do I need to modify the code structure of test suite Request?

I prefer to keep the same for now. Different tools might be different struct. It's impossible to match all of them.

[LinuxSuRen]

I have tested it. It works well. See my steps:

And happy to have you as the 20th contributor.