HX-Boost is not always sent in all AJAX requests that htmx sends, only
those initiated by an element with hx-boost enabled. It was not showing
up on requests following an HX-Redirect response.
After reading the docs more, I realized HX-Target was what I wanted. If
I can see that the request is targeting `#main-content` then I know to
only return HTML inside that element. Simple.
