Check multipicture views generation updates

In order to secure NXP-28434, we need to check for each document if the multipicture generations have been updated properly

We could reset all picture views with the placeholder (empty_picture) and check the digest to be sure it has been updated (maybe already done! https://github.com/nuxeo/nuxeo/blob/10.10/nuxeo-features/nuxeo-platform-imaging/nuxeo-platform-imaging-core/src/main/java/org/nuxeo/ecm/platform/picture/listener/PictureChangedListener.java#L84)

Think just about checking the digest and not the filename?