Push custom images used in XWiki docker tests on docker hub

We currently build custom docker images for testing XWiki Platform with libreoffice. Those images are built whenever they are needed in docker test, if the image is not already locally available. This means that if the image is locally available it will never be refreshed, even if some changes are made in the way the image should be built.

We shouldn't build those images as part of our test since it's costly and we don't master properly the way a new image should be used. Instead we should push those custom images on docker hub and rely on them.

The code for building those images can be found there: https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-test/xwiki-platform-test-docker/src/main/java/org/xwiki/test/docker/internal/junit5/servletengine/ServletContainerExecutor.java#L222