How to add button for source code view to editor toolbar in Moodle?

I tried to get some information on how to get a richer toolbar on H5P questions in Moodle, but I just couldn't figuere it out. On the bottom line, I need a button to display HTML source code instead of WYSIWYG. I know that CKEditor has this functionality, but how can I enable it on textareas in H5P questions on Moodle?

If possible for all content types, this woule be good, otherwise on a per content type basis.