Add multilevel navigation menu (navigation tabs) for Quarto websites

[AshleyHenry15]

Description

Now that we are using Quarto to publish our product documentation, we need to add "support" for additional organization since we are merging all of our product's guides into a single documentation site.

Although we have the ability to add "navigation tabs" to the nav bar for each guide, we are quickly running out of room on the nav. Additionally, when the page/browser window resizes, it causes unnecessary wrapping, etc.

MkDocs offers this using "navigation tabs": https://squidfunk.github.io/mkdocs-material/setup/setting-up-navigation/?h=navigation+tabs#navigation-tabs

Please see the Package Manager docs for a "live" example: https://docs.posit.co/rspm/admin/

Currently, our Connect documentation site looks like this:

I am proposing to add support to drop the guides/tabs down a level on the nav and have it look something like this: