RJS: fix joomla associations being lost - add a propagate button

[shoulders]

• https://youtu.be/EdQOpQ2IzXM?t=2022 - this alternative button is in his alt code
• https://youtu.be/EdQOpQ2IzXM?t=2130 + propagate.js ajax.json.php + shows his alt code

This section handles adding a button to disemminate file associations from with an item

• https://youtu.be/EdQOpQ2IzXM?t=2123 - propagate button code

• https://youtu.be/EdQOpQ2IzXM?t=2150 - propagate.js is mentioned

• https://youtu.be/EdQOpQ2IzXM?t=2200 - example of controller name

• https://youtu.be/EdQOpQ2IzXM?t=2221 - controller shown /admin/controllers/ajax.json.php he has call his `ajax.propogagte' ?

• https://youtu.be/EdQOpQ2IzXM?t=2292- stuck or just want to look at the answer [New Feature] Multilingual: Propagating existing associations if desired joomla/joomla-cms#21321

• full merge details joomla/joomla-cms@11153f7 for com_content and other core

ps.s has this feature now been added to the core