[Feature]: Docs - Add ability to hide a tab

[magaldima]

Problem description

Currently with the TabbedNavigation, it is impossible to hide tabs.

Why would it be useful?

I want to use Fern to develop an entirely different API that is exposed to a different client audience than our existing one. Ideally, I want this API to only be accessible by a link so that most users who interact with our docs do not see it and get distracted.

Describe the solution (optional)

Be able to mark tabs as hidden whereby they do not show up in the Tab Navigation bar but if i go directly to the path/slug, I can view the contents of the entire tab.