Make sure summer-cleaner.js comes after the other Summernote .js files - I think this might be the cause of the error you mention.
Adding the options in script tags as you suggest should work. You’ll need to add the ‘cleaner’ to one of the toolbar groups, eg:
['font',['bold','underline','clear','cleaner']]
It almost works very well, but there seems to be a serious problem - the script disables the ability to paste into the Summernote textarea. If you drag/drop formatted text from Word and click the ‘cleaner’ button, it does a good job of cleaning the code, but the option to copy/paste needs to work too.
I found some references to the error when pasting:
summernote-bs4.min.js:2 Uncaught TypeError: Failed to execute 'setStart' on 'Range': parameter 1 is not of type 'Node'.
… and a suggestion that the problem had been fixed, but perhaps it hasn’t. It’s quite possibly that I haven’t added the plugin correctly. Let me know if you get it working.