Add Dockerfiles for clients

.dockerignore

Dockerfile

clients/README.md

clients/consumer-3/Dockerfile

clients/consumer-3/Makefile

clients/consumer-3/docker-entrypoint.sh

clients/producer-1/Dockerfile

clients/producer-1/Makefile

clients/producer-1/docker-entrypoint.sh

clients/producer-3/Dockerfile

clients/producer-3/Makefile

clients/producer-3/docker-entrypoint.sh

docker/flink/Dockerfile