Bugfix: Purge cache upon updating image details

We discovered a minor bug where updating image title, caption, or alternative text for an image within the media manager did not trigger an automatic purge of the site cache as expected.

Not purging the cache when making this kind of change would mean that outdate information remains visible on the website.

This issue was addressed; the site cache is now purged when making this kind of change, meaning that changes to image details are now immediately visible on customer's websites.