Respect the DoNotTrack header

Vincentrequested to merge
88-prevent-confidence-checks-from-showing-up-in-analytics into dev

This prevents Google Analytics from being added to the page when the user has enabled DoNotTrack.

It's supposed to also enable DoNotTrack for both Firefox and Chrome when started by WebdriverIO (e.g. in the automatic confidence checks in CI), but that does not appear to work. Since it's not that important yet, I'll leave it at that for now.

Merge request reports