HttpRequest.is_ajax() was marked as deprecated since Django 3.1 and will be
removed in Django 4.0 [1].
While the current implementation of is_ajax() relies on a jQuery-specific way
of signifying AJAX as noted in the Django relnotes, horizon works with this.
Thus this commit copies the existing logic of HttpRequest.is_ajax() to the
horizon repo (as horizon.utils.http.is_ajax()) and consumes it.
https: //docs.djangoproject.com/en/4.0/releases/3.1/#features-deprecated-in-3-1
Change-Id: I3def53033524985818a891a1b9d4659fad4ba2ba
7052b7f065