Add a template folder path in the open api client generator

[JMalaval]

Hello 👋

I need to use your package so first of all thanks you very much for created it 🙏

I just need to add an option to add a folder template path. As you maybe know we can use template written in mustache in openapi client generator, an use it tu customize your package.json or any file you want. But its not added in your package so maybe you can add it please ?

I can write the PR if you want or just give you the code if you prefer, I shared it tou you.
You just need to add that

        options?.templateFolderPath
          ? `-t \"${options.templateFolderPath}\"`
          : '',

in src/openapi-client-generator/openapi-client-generator.service.ts

And obviously the templateFolderPath option in the type 😄