Is it possible to have those URL query parameters embedded or auto-generated in a field within AEM authoring when building a landing page, so that we don't need to enter manually per internal campaign? And what is the best way to go about it?
If I understand the requirement here, you are trying to read the values from certain parameter and store those values in AEM page properties which you want to do it only while authoring.
If this is the requirement, you can do it using the Sling Model in Java. You just need to create a model class which will read the query parameter value (whichever you want) and then set those values into AEM page property with respective name.
Now you need to ensure that this logic should work only on author instance and in edit mode, so you can add the necessary condition checks in sling model to for WCMMode.Edit and Runmode author.
Once you have the logic in place, when you open any page with edit mode and have the requried query param in the URL, the values will be automatically set in the page properties and once you publish the page, the same content will be replicated to publish instance. For validation you can open the page property and check the custom tab, you should be able to see the query param values.