Add Dockerfile, gitlab-ci

.gitlab-ci.yaml

+stages:
+  - build
+  - deploy
+
+services:
+  - docker:dind
+
+variables:
+  DOCKER_HOST: tcp://localhost:2375
+
+build:
+  image: docker:latest
+  stage: build
+  script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+    - docker build -t ${CI_REGISTRY}/${CI_PROJECT_NAME}/polls:${CI_COMMIT_SHORT_SHA} .
+    - docker tag ${CI_REGISTRY}/${CI_PROJECT_NAME}/polls:${CI_COMMIT_SHORT_SHA} ${CI_REGISTRY}/${CI_PROJECT_NAME}/polls:latest
+    - docker push -- ${CI_REGISTRY}/${CI_PROJECT_NAME}/polls
+  tags:
+    - k8s