feat: extend filesystem (#1699)

* fix: use `relative_path` for file entry info

* docs: type

* feat: extend filesystem to fully support directories

* feat: a specific dir for each filesystem entity (files, dirs)

* test: templating

* test: move test-only impls to test module

* test: templating

* test: proper yaml rendering

* docs: detail how this module works

* feat: SafePath -> PathBuf

* feat(rendering): generate writable file list

* feat: rendering filesystem entry list

* style: rename path field

* test: rendering expected file entries

* test(integration): fix filesystem ops

Author: DavSanchez