add kaniko based docker image builds

.gitlab-ci.yml

-image: golang:1.12
+image: golang:1.13
 
 
 cache:
@@ -80,3 +80,16 @@ build:
   artifacts:
     paths:
       - tank
+
+docker:
+  stage: build
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
+  script:
+    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination aura/tank:$CI_COMMIT_TAG --tarPath $CI_PROJECT_DIR/docker.tar
+  only:
+    - master
+  artifacts:
+    paths:
+      - docker.tar

Dockerfile

 ### Build Image
-FROM golang:1.12-buster
+FROM golang:1.13-buster
 MAINTAINER Christian Pointner <equinox@helsinki.at>
 
 RUN set -e \