Add tooltip to shortcut element in navbar search field

Problem to solve

This is a follow-up to #342427 (closed) / !84085 (merged) where we added a shortcut keyboard element (kbd) to the navbar search field to increase the visibility of the shortcut.

Some users may not understand what this element is in the search field and why it is there.

Proposal

Include a tooltip with the shortcut element to explain what this is how they can use the shortcut.