Manual controls to expand, collapse, and minimize the left nav

[eric-schneider]

In the old UI, we provide manual controls for the following:

• Minimize or expand the entire left nav (more important of the two behaviors)
• Expand or collapse all nested items in the left nav

This feature was added at the request of a few internal users, and is something we should at least consider adding back to the new UI. The Astra Portal allows manual control to minimize/expand the left-nav, but the new docs UI only offers this control at smaller screen widths.