Improve keyboard navigation for search

[johnbillion]

Two enhancements would be nice for the search feature on https://docs.altis-dxp.com/.

1. Support ⌘K / CtrlK for opening the search box
2. Support ↑ and ↓ arrows for navigating search results (in addition to tab)

[mikelittle]

This should be looked as part of the new documentation system