feat(file_system): Update example to include built+bundled file system

[finger563]

Description

• Adds directory of files to example which is built and bundled onto the target
• Fixes minor bug in espp::FileSystem::list_directory string output

Motivation and Context

Often it is useful to pre-populate an embedded file system with data from the host file system. This example now showcases how easy it is to do.

How has this been tested?

Building and running file_system/example on a QtPy ESP32s3.

Screenshots (if appropriate, e.g. schematic, board, console logs, lab pictures):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Documentation Update
• [ ] Hardware (schematic, board, system design) change
• [x] Software change

Checklist:

• [x] My change requires a change to the documentation.
• [x] I have added / updated the documentation related to this change via either README or WIKI

Software

• [x] I have added tests to cover my changes.
• [ ] I have updated the .github/workflows/build.yml file to add my new test to the automated cloud build github action.
• [x] All new and existing tests passed.
• [x] My code follows the code style of this project.

[github-actions[bot]]

:white_check_mark:Static analysis result - no issues found! :white_check_mark: