Add docker build in CI

.gitlab-ci.yml

+image: docker:19.03.12
+services:
+  - docker:19.03.12-dind
+
+stages:
+  - build
+  - test
+
+variables:
+  CONTAINER_RELEASE_IMAGE: $CI_REGISTRY_IMAGE:latest
+
+before_script:
+  - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
+
+build:
+  stage: build
+  script:
+    - docker build --pull -t $CONTAINER_RELEASE_IMAGE .
+    - docker push $CONTAINER_RELEASE_IMAGE
+
 checker:
+    stage: test
     image:
-        name: jokeswar/perfect-assignment
+        name: $CONTAINER_RELEASE_IMAGE
     script:
         - echo ""