US: Publish app docker images in GitHub packages

[eljamm]

Description

As a < type of user >, I want < some goal > so that < some reason >.

Acceptance criteria

• Given < some context >, when < some action is carried out >, then < set of observable outcomes should occur >.

Notes

• https://github.com/ngi-nix/openfoodfacts-server/pkgs/container/openfoodfacts-server%2Fbackend
• https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry