ref of docker.elastic.co for local images

[nagkumar]

_favorite-java-elastic-manual:
    build: java-favorite-elastic-manual/.
    image: docker.elastic.co/demos/workshop/observability/elastiflix-java-favorite-elastic-manual:${ELASTIC_VERSION}-${BUILD_NUMBER}_

&

_favorite-java-elastic-auto:
    build: java-favorite-elastic-auto/.
    image: docker.elastic.co/demos/workshop/observability/elastiflix-java-favorite-elastic-auto:${ELASTIC_VERSION}-${BUILD_NUMBER}_

as these are built image should not point to docker.elastic.co

[nagkumar]

It is ideal to remove image attribute to clearly say using locally built image only