Hello and welcome! Glad to have you here.
No, as far as I can tell this post_liked webhook never was added. I think post_liked is a fairly low value bit of information to go to the trouble of firing a webhook, tbh.
The community I was working with when I wrote that post has a procedure to periodically export activity via the data explorer plugin and then import it to their external tracking dashboard. Works quite well and allows a bit of gardening before import (e.g. to remove activity in private categories).. just isn’t immediate. 
That said, I haven’t played with this personally for a while. Looks like there is a “Notification event” option which might work. Users are notified when their posts are liked unless they muted the topic.
I’d suggest spinning up a discourse instance and trying it out! Let us know how it goes.
