What makes Ctrl+Q work in zsh

Question

I'm a zsh user who started off with a plain oh-my-zsh configuration and now I try to learn zsh by importing the parts I care about from oh-my-zsh into my own .zshrc and then completely remove oh-my-zsh.

When I now finally went cold turkey and removed oh-my-zsh I noticed that one of my most used shortcuts, Ctrl+Q has stopped working. I've investigated this and found the command to be called push-line according to this source.

I have no idea how to start using that ZLE feature though. I'm not even sure how to check if zle is running or not. I tried for hours to try to search the oh-my-zsh repository, but haven't found the command that activates push-line.

What do I need to do to get Ctrl+Q working? What is it that oh-my-zsh does that I need to put in my own zshrc?