The documentation page "Modifying an Editor's Configuration" in dev.liferay.com is not valid for CKEditor
The sections 5 and 6 of that page about how modify a toolbar, are only valid for AlloyEditor:
In the populateConfigJSONObject method, you need to instantiate a JSONObject that holds the current configuration of the editor. For instance, you could do something like this:
JSONObject toolbars = jsonObject.getJSONObject("toolbars");
This gets the editor's toolbar. Now that you've retrieved the toolbar, you can modify it. You'll do this next.
You'll modify the editor's toolbar by adding a camera button. To complete this, extract the Add buttons out of your toolbar configuration object as a JSONArray, and then add the button to that JSONArray. The following code adds a Camera button to the editor's toolbar:
It is necessary to modify that page and add the information about how to personalize toolbars in CKEditor or at least, add a warning saying that code is only valid for AlloyEditor.