Use Docker multi-staged builds

[rosle]

Because we're having the problem with the image layers limitation on Heroku, happens with the application that has many engines - #180. We could make a use of docker multi-staged builds to build the image.

We can have a stage where we install the dependencies and we copy those files into the final image. For each stage we need to push to the registry for caching.

This will remove an extra step we need to do in order to build the image.

[andyduong1920]

Just an example https://github.com/nickjj/docker-rails-example/blob/main/Dockerfile