Support privacy improvements for Google Analytics

[mthmulders]

This pull requests copies the internal Google Analytics template that ships with Hugo 0.41 and higher. It supports a few improved privacy options.

Alternatively, instead of copying (and slightly modifying it), we could do

{{ template "_internal/google_analytics.html" . }}

But this does not work with Hyde currently. It would mean that the Google Analytics key needs to move:

# new location
googleAnalytics = "UA-XXXXXXXX-X"

# old location
[params]
googleAnalytics = "UA-XXXXXXXX-X"

This would break for existing users of Hyde, so it might or might not be a good idea. The benefit is that Hyde will automatically use improvements in the Hugo built-in Google Analytics integration, the drawback is that users need to update their config.