Rich text widget extra plugin

Hello Guys,

I am new to apostrophecms, so I don't know the details of this technology. As there is a rich-text widget that uses the CKEditor plugin. So I have followed the instructions from the following URL to add an external plugin:

https://docs.apostrophecms.org/howtos/ckeditor.html#global-ckeditor-configuration

I am trying to add below plugin from CKEditor:
https://ckeditor.com/docs/ckeditor4/latest/features/sourcearea.html

When I have completed all the steps it doesn't show any error and not showing the plugin in the toolbar.

So please help me.

Start by reproducing the issue in the ApostropheCMS rich-text widget using the global CKEditor configuration instructions and the CKEditor Source Editing plugin documentation. Confirm whether the external plugin loads and whether its control appears in the widget toolbar; document the configuration or compatibility issue that prevents it from appearing.

Written by the indexing model from the issue text.