What is old is new again :) Back when I started development, we did this via git remotes, and some projects even did what you created and created environments mapped from git remotes to apps running with subdomains (like Dokku is probably the first/most memorable FOSS service for this back in the day).
And before that, I'm sure people were doing the same thing with Java WARs or similar, and before that, something else but similar.