Implementation docker for production deploy

[antoineludeau]

This pull request aims to prepare implementation of the adresse.data.gouv docker image for production by :

• Defining the production image (Dockerfile)
• Defining the github workflow to build and push the image in the Docker Hub, the job being triggered at each push in the 'master' branch (and so, during each merge into master)

What still need to to done (that's why the pull request is still in DRAFT mode) :

• Create a BAN registry in DockerHub (example: ban/adressedatagouv). We can create a free Docker Hub account for the BAN open source community (limit = 200 container image requests per six hours).
• Add github secret to login to the docker hub registry : DOCKERHUB_USERNAME and DOCKERHUB_TOKEN

That done, the only command that will need to be started on the ban-server will be :

docker run -p 5100:5100 --env-file ./app-env ban/adressedatagouv

Comments on the above command
-p 5100:5100 = mapping inner docker container port 5100 to external port 5100
--env-file ./app-env = Inject env variable from the file 'app-env' (file can have another name)