Install using OCI (Docker) images

We provide the following OCI images:

• registry.gitlab.com/fediventure/fediventure/workadventureback:main - backend
• registry.gitlab.com/fediventure/fediventure/workadventurefront:main - frontend
• registry.gitlab.com/fediventure/fediventure/workadventurepusher:main - pusher

TODO(q3k): describe how to configure/deploy this