Add HEALTHCHECK in Dockerfile

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Add a Docker Healthcheck to the Dockerfile. See this example : https://github.com/docker-library/healthcheck/tree/master/postgres

Reference :

• https://docs.docker.com/engine/reference/builder/#healthcheck

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To test HEALTHCHECK command in image :

docker inspect --format="{{json .Config.Healthcheck}}" IMAGE_ID

To test HEALTHCHECK status in container :

docker inspect --format="{{json .State.Health.Status}}" CONTAINER_ID