Add gitlab ci workflow to build docker image

Change-Id: Ibdd497d7645a36534542d2896251393eea36248c

.gitignore

@@ -2,6 +2,7 @@
 !/.gitignore
 !/.github
 !/.dockerignore
+!/.gitlab-ci.yml
 target
 tmp
 logs

.gitlab-ci.yml

@@ -0,0 +1,31 @@
+# gitlab ci pipeline to build kustvakt docker container
+# automatically triggered on tag pushs or run manually
+#
+# Download latest container from artifacts and import it:
+#
+# curl -Ls 'https://gitlab.ids-mannheim.de/KorAP/kustvakt/-/jobs/artifacts/master/raw/kustvakt.tar.xz?job=build-docker' | docker load
+
+image: docker:latest
+
+services:
+  - docker:dind
+
+build-docker:
+  rules:
+    - if: $CI_COMMIT_TAG =~ /.+/
+      variables:
+        VID: $CI_COMMIT_TAG
+    - when: manual
+      variables:
+        VID: $CI_COMMIT_BRANCH-$CI_COMMIT_SHORT_SHA
+  stage: build
+  before_script:
+    - apk update
+    - apk add --no-cache git
+  script:
+    - docker build -f Dockerfile -t korap/kustvakt:$VID -t korap/kustvakt:latest  -t korap/kustvakt:$VID-full -t korap/kustvakt:latest-full --target kustvakt-full .
+    - docker save korap/kustvakt:$VID-full | xz -T0 -M16G -9 > kustvakt.tar.xz
+  artifacts:
+    paths:
+      - kustvakt.tar.xz
+