Add PlantUML CI

.gitlab-ci.yml

+default:
+  image:
+    name: plantuml:2.0
+    entrypoint: ["/bin/sh", "-c"]
+  tags:
+    - shared-fi
+
+create-diagrams:
+  before_script:
+    - apk add --no-cache git
+    - git config --global user.name "${GITLAB_USER_NAME}"
+    - git config --global user.email "${GITLAB_USER_EMAIL}"
+    - mkdir -p docs
+  script:
+    - java -jar /usr/diagrams/plantuml.jar -failfast -o $(pwd)/docs "*/*.puml"
+  after_script:
+    - |
+      git add -f docs/*.png
+      git commit -m "feat(docs): update-diagrams ✔️" || echo "No changes, nothing to commit!"
+      git remote rm origin && git remote add origin http://root:$ACCESS_TOKEN@gitlab.fi.muni.cz/$CI_PROJECT_PATH.git
+      git push origin HEAD:$CI_COMMIT_REF_NAME
+  rules:
+      - if: '$CI_PIPELINE_SOURCE == "merge_request_event" && $CI_COMMIT_MESSAGE !~ /update-diagrams/'
+        when: manual
+  artifacts:
+    paths:
+      - "docs/*.png"
+    expire_in: 7 days