Investigate multi-level / nested doc indexing

[erikaheidi]

This would be ideal for multi-language documentation and to support nested content.

[erikaheidi]

PR open to add support for multi-level content dirs in librarian-core. still needs some work in this repo to confirm that URLs and navigation are functional.

[erikaheidi]

From the content side, it's all functional, but more work needs to be done in the Request class to support listing pages for sub-levels of content. Currently working on tests for the Request class and will improve it from there.

[erikaheidi]

Next, update command-web where the web controllers live

• add tests for nested content
• use getParent for obtaining the Content Type
• verify that post lists are correctly obtained in sub-levels