It is the app formally named "workflow" that apple acquired some time ago. It got renamed to "shortcut" for iOS 12 and has this ssh action in it.
If you already had the old "workflow" app it will be updated to the new "shortcut" app, if you do not have it you need to install it from the App Store.
I am familiar with shortcuts, but I didn't think that there was an actual SSH action that was shipped with it, I thought there was an SSH action that an application may be providing.
If you already had the old "workflow" app it will be updated to the new "shortcut" app, if you do not have it you need to install it from the App Store.