Use Docker Buildpacks image support from Spring Boot

[arey]

Allowed by the PR #247 we could now use the Cloud Native Buildpacks with the command line:

./mvnw spring-boot:build-image 

See https://spring.io/guides/topicals/spring-boot-docker/

To build a Docker image, we can propose 2 options :

1. keeping Dockerfile support with the buildDocker Maven profile
2. use the Spring Boot maven build-image plugin

Buildpacks image does not provide curl for health check (used in the docker-compose.yml). Thus we have to install another health check tool that we don't have in the Dockerfile: https://github.com/paketo-buildpacks/health-checker