Add storage path permissions test

[bryanlopezinc]

Description

Add storage path permissions test for SettingsController@getSetupIndex

Checklist:

• I have read the Contributing documentation available here: https://snipe-it.readme.io/docs/contributing-overview
• I have formatted this PR according to the project guidelines: https://snipe-it.readme.io/docs/contributing-overview#pull-request-guidelines
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[what-the-diff]

PR Summary

• Enhancement of Storage Path Verification
  The SettingsController.php file now includes a method that checks if the application storage path can be written to. This improvement ensures that the system only attempts to write to storage paths that are writable, preventing any unwarranted system errors.

• Improved Error Handling and User Communication
  In case of directory permission errors (when the storage path is not writable), an appropriate error message will be displayed, contributing to a better understanding of the issues the system may encounter.

• Intensive Testing for Permission Errors
  Multiple test cases have been added to ShowSetUpPageTest.php to thoroughly test the above changes. These tests focus on verifying the accurate display of directory permission errors and ensuring that no errors are displayed when the storage path is writable, enhancing the robustness and error-free operation of the software.

[snipe]

This looks great, thank you!