Build docker images

Build docker images for robert-server-ws-rest, robert-crypto-grpc-server, and tac-warning-ws-rest

When build on the develop branch the docker images are pushed in this project registry ie. access via

docker login registry.gitlab.inria.fr
docker pull registry.gitlab.inria.fr/stemcovid19/tac-server/backend-server/robert-server-ws-rest:latest
docker pull registry.gitlab.inria.fr/stemcovid19/tac-server/backend-server/robert-crypto-grpc-server:latest
docker pull registry.gitlab.inria.fr/stemcovid19/tac-server/backend-server/tac-warning-ws-rest:latest

Note: this rely on a personal access token hidden in the CI configuration in order to login into docker.io registry and successfully pull store/oracle/serverjre:8