Add priv_dir functions to return priv directory

[shahryarjb]

Hello Dear igniter team,

Based on the discussion we had in the Ash Discord, I added this app_name() combination function to the project to return priv directory.

This priv_dir function simply improves convenience and consistency when working with igniter.

I hope I followed the project format correctly and do not waste your time, as it was a bit different from my usual coding style 🥹.

If there are any issues, please let me know so I can address them.

Contributor checklist

• Features include unit/acceptance tests

[zachdaniel]

🚀 Thank you for your contribution! 🚀