[feat] Provide a docker image for the app

[anarion80]

It would be great if there was a docker image for the app available, with corresponding docker-compose file to quickly set it up on docker.

Once docker image is available, some simple github image action could also be added. Something like: https://github.com/anarion80/ghost_cloudinary_docker/blob/main/.github/workflows/build-and-publish.yml

[pkarw]

Thanks @anarion80! Happy to accept such a PR - otherwise it will probably wait a while in the queue, but it's definitely good idea!