Include Handbook search bar on company and culture pages

@BarbieGitLab, this is a bit of a hack-y first iteration at including the culture pages in our handbook search. This MR should start including the search bar at the top of all pages under the company and culture directories, but it doesn't actually expand the search results just yet to include pages outside of the handbook, which will be the next, more complex iteration, possibly as part of the integration of a new search tool.

I still think there's some value in including the bar at the top of these pages as it allows for quick navigation from them to other pages that actually are in the Handbook, so I'm pushing this iteration forward now.