[Feature Request] add responsive navigation

[Arhell]

Is your feature request related to a problem? Please describe.

Describe the solution you'd like
Add the ability to change navbar-expand-md to navbar-expand-lg and other options in docfx.json.

Additional context
If the navigation menu is large there is no way to change this.

[yufeih]

The search box takes too much width, we could default to navbar-expand-lg and collapse the search box into an icon as needed.

[Arhell]

The search box takes too much width, we could default to navbar-expand-lg and collapse the search box into an icon as needed.

Did I understand correctly that I will need to take the layout and change it there?
Example https://github.com/dotnet/docfx/blob/main/templates/default/partials/navbar.tmpl.partial

I just suggest doing this in the 1st file as I wrote in the first post docfx.json