CI now pushes to and pulls from Docker Hub

.gitlab-ci.yml

-workflow:
-  rules:
-    - if: '$CI_COMMIT_TAG'
-      when: never
-    - when: always
 stages:
   - tag_version
   - build
   - ci
   - coverage
+variables:
+  BACKEND_IMAGE: $CI_REGISTRY_USER/mcserver:latest
+  FRONTEND_IMAGE: $CI_REGISTRY_USER/mc_frontend:latest
+workflow:
+  rules:
+    - if: '$CI_COMMIT_TAG'
+      when: never
+    - when: always
 tag_version:
   image: python:3.8-alpine
   stage: tag_version
@@ -21,8 +24,11 @@ build:
     - docker:20.10.8-dind
   stage: build
   script:
-    - docker build ./mc_frontend -t machina_callida/mc_frontend:latest
-    - docker build ./mc_frontend -t machina_callida/mcserver:latest
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
+    - docker build ./mc_frontend -t $FRONTEND_IMAGE
+    - docker push $FRONTEND_IMAGE
+    - docker build ./mc_frontend -t $BACKEND_IMAGE
+    - docker push $BACKEND_IMAGE
   variables:
     DOCKER_DRIVER: overlay2
     DOCKER_TLS_CERTDIR: ""
@@ -36,7 +42,7 @@ ci_frontend:
     - docker:20.10.8-dind
   stage: ci
   script:
-    - docker run --rm --entrypoint="npm run test-ci" machina_callida/mc_frontend:latest > ci_frontend.log
+    - docker run --rm --entrypoint="npm run test-ci" $FRONTEND_IMAGE > ci_frontend.log
   variables:
     DOCKER_DRIVER: overlay2
     DOCKER_TLS_CERTDIR: ""
@@ -50,7 +56,7 @@ ci_backend:
     - docker:20.10.8-dind
   stage: ci
   script:
-    - docker run --rm --entrypoint="./coverage_backend.sh" machina_callida/mcserver:latest > ci_backend.log
+    - docker run --rm --entrypoint="./coverage_backend.sh" $BACKEND_IMAGE > ci_backend.log
   variables:
     DOCKER_DRIVER: overlay2
     DOCKER_TLS_CERTDIR: ""