## About the changes
Instead of building from source (we require Node 18 but [DigitalOcean
buildpack currently does not support
it](https://www.digitalocean.com/community/questions/app-platform-node-build-pack-can-t-use-node-version-18)),
we're going to use our Docker image from DockerHub:
https://hub.docker.com/r/unleashorg/unleash-server
Additionally, I realized that our Dockerfile only works in our CI (or
performing a pre-build step which consists of building the frontend).
With this PR I've also made a change to build the frontend if needed.
That way our CI will continue to be optimal while anyone trying to build
it from source will be able to do it by just running `docker build .`
Closes#4261