Move container_registry user docs to new location

doc/administration/container_registry.md

doc/container_registry/README.md

doc/container_registry/img/container_registry.png

doc/container_registry/img/project_feature.png

doc/container_registry/troubleshooting.md

doc/user/project/container_registry.md

doc/user/project/img/container_registry_enable.png

doc/user/project/img/container_registry_panel.png

doc/user/project/img/container_registry_tab.png

doc/user/project/img/mitmproxy-docker.png