feat: add `log.FilePath()` function for logger

[DmitriyLewen]

Description

We often use log.String() with file/filepath/path/etc. key for filepath. Add log.FilePath() function to use a consistent key name.

Checklist

• [x] I've read the guidelines for contributing to this repository.
• [x] I've followed the conventions in the PR title.
• [ ] I've added tests that prove my fix is effective or that my feature works.
• [ ] I've updated the documentation with the relevant information (if needed).
• [ ] I've added usage information (if the PR introduces new options)
• [ ] I've included a "before" and "after" example to the description (if the PR is a user interface change).