New Rule to find orphan files

[trunneml]

Summary

This Pull Request introduces a new rule that identifies orphan files within a specified folder. These orphan files are assets that are no longer referenced in any scanned Markdown file, contributing to clutter in the documentation directory.

Changes Made

To achieve this, a new method has been added to the plugin_manager that is triggered after all files are scanned. This method triggers the plugin that then identifies assets within the specified folder that are not referenced, allowing for their removal.

Reasoning

By implementing this rule and introducing the new method in the plugin_manager, we can proactively clean up the documentation directory by identifying and removing orphan files. This contributes to improved organization and maintainability of the project. The rule helps ensure that only relevant and referenced assets are present, reducing confusion and clutter for developers and contributors.