Include Cheaha Storage (GPFS) nav branch in two places

[wwarriner]

In our nav, we have Cheaha Storage (GPFS) as a branch.

Let's find a way to include this under Data Management and under Cheaha Guide.

• The underlying files would not be duplicated, instead we would merely duplicate the nav branch of file references and nav titles.
• Ideally, we would have a single definition of the nav branch, and reference it from two places in the nav. It may be possible to achieve this with the "Literate Nav" plugin https://github.com/oprypin/mkdocs-literate-nav and macros, depending on plugin callback execution order.

[wwarriner]

Mkdocs Literate Nav Plugin

In base mkdocs, the site navigation panel is built from the nav: section of mkdocs.yml. This data takes the form of a tree and is fully explicit.

We want to re-use branches of our nav tree. Specifically, we want the "Cheaha Storage" branch of the nav tree to appear under both Data Management and under Cheaha Guide. To do so would require the nav to be capable of handling implicit references.

The Literate Nav plugin should be able to do this out of the box. The way the plugin works is by shifting nav definition to one or more markdown files containing lists of internal links. You can have each directory in the docs files contain its own nav markdown file. Then, top-level markdown files can contain nested markdown files twice in the following way.

docs/data_management/cheaha_storage/SUMMARY.md

- [page](page.md)
- [page2](page2.md)

docs/cheaha_guide/SUMMARY.md

- [page3](page3.md)
- [Cheaha Storage](../data_management/cheaha_storage/)

docs/SUMMARY.md

- [Data Management](data_management/)
- [Cheaha Guide](cheaha_guide/)

This generates a nav with this structure:

- Data Management
    - Cheaha Storage
        - page
        - page2
- Cheaha Guide
    - page3
    - Cheaha Storage
        - page
        - page2

The filename is flexible, and the feature can be mixed with the traditional nav. Since I want to move nav out of mkdocs.yml in any case, this works for me.