Install a plugin to Liferay's editor

Question

I have a Liferay DXP installation and I would like to install a plugin to the editor. The plugin is base64image.

I was following this official guide so I created a class generally like this:

@Component(immediate = true, service = DynamicInclude.class)
public class CKEditorBase64ImageDynamicInclude implements DynamicInclude {

        private BundleContext bundleContext;


        @Override
        public void include(HttpServletRequest request, HttpServletResponse response, String key) throws IOException {
                Bundle bundle = bundleContext.getBundle();
                URL entryURL = bundle.getEntry("/META-INF/resources/html/editors/ckeditor/extension/base64_images.js");
                StreamUtil.transfer(entryURL.openStream(), response.getOutputStream());
        }

        @Override
        public void register(DynamicIncludeRegistry dynamicIncludeRegistry) {
                dynamicIncludeRegistry.register("com.liferay.frontend.editors.web#ckeditor#onEditorCreate");

        }

        @Activate
        protected void activate(BundleContext bundleContext) {
                this.bundleContext = bundleContext;
        }

}

It should include the base64_images.js file where it initializes the editor. But it never works, regardless what the content of the file is. What is wrong with that?

I would like to add that the plugin files (JavaScript code) are part of my Liferay theme. I wanted base64_images.js to call its API but it also might not be the correct way how to do it.