Tracking Outbound Clicks with Google Analytics?

Hello!

I am trying to add outbound click tracking via GA for my website. I came across this guide which explains how to do it: https://support.google.com/analytics/answer/1136920?hl=en

The execution is simple, but given the size of my site unattainable, since I would need to add the onclick element to every external link for it to work.

My question: How can add the required onclick element for tracking to every external link with a plugin, function, or other automated means?

Thanks in advance!