Easiest way to add a "source code" button to the CK Wysiwyg/ HTML-Editor?

EDIT: Sorry if this is a duplicate. I posted this in the feature request forum but the post there is not publicly available. 

I really dislike the decision to not provide a html button in the CK editor. Adding images is not possible in most areas but could easily be accomplished with a little HTML. Unfortunately there is no button to switch to the "source view" which makes editing and customization of questions and anwsers nearly impossible.

I was able to globally insert options for creating links and tables - I really don't get why these basic things where not allowed in the first place. Anyways, as images in answers or feedback-texts are not allowed the "native h5p way" - what is the easiest solution to provide a source button or even better an image button where I can easily insert an image url?

Thanks in advance and sorry if this post sounds annoyed. But I totally disagree on these decisions and have no understanding for them whatsoever.