#460, second MR to fix filesystem dependency for akeneo

This should be reviewed after !465 (merged)

This MR will solve the http->http redirect loop for images that arises when the httpd process doesn't see the image files that are in the php container (aka pcmt/fpm). This solves that by moving all of the files into the filesystem of one container, and then sharing those files via a docker volume to the other container. In this case everything is packaged into the pcmt container, and shared read-only to the httpd container.

Once merged this can be verified by starting pcmt locally (e.g. make up) and seeing if the product images no longer have broken links.