ci(kOS): Unify build pipelines after global switch to Podman

This patch re-unifies the build pipelines for images including kOS to use
a central CI definition instead of a specific one for kOS.

.gitlab-ci.yml

 ---
 include:
   - local: 'images/.utils/gitlab-ci.yaml'
-  - local: 'images/kos/.gitlab-ci.yaml'
   - local: 'charts/.utils/gitlab-ci.yaml'
 stages:
   - lint

images/.utils/gitlab-ci.yaml

@@ -7,6 +7,7 @@
           - koolbox
           - synadm
           - query-exposer
+          - kos
 
 container-build-release:
   stage: build

images/kos/.gitlab-ci.yaml

-### This separate build pipeline is required, because rpm-ostree and kaniko don't work together as expected.
-build-kos:
-  stage: build
-  image: quay.io/containers/podman:v4.3.1
-  variables:
-    CI_REGISTRY_IMAGE: quay.io/shivering-isles/kos
-  before_script:
-    - podman login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-  script:
-    - podman build --pull
-      --label "org.opencontainers.image.source=$CI_PROJECT_URL/-/tree/$CI_COMMIT_SHA/images/kos"
-      --label "org.opencontainers.image.revision=$CI_COMMIT_SHA"
-      --label "org.opencontainers.image.title=kOS"
-      --label "quay.expires-after=12w"
-      -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
-      --format docker
-      images/kos
-    - podman push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
-    - podman push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA" "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
-  rules:
-    - if: '$CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH && $CI_PIPELINE_SOURCE == "push"'
-      changes:
-        paths:
-          - images/kos/**/*
-        compare_to: main
-  tags:
-    - hetzner
-
-### This separate build pipeline is required, because rpm-ostree and kaniko don't work together as expected.
-build-kos-release:
-  stage: build
-  image: quay.io/containers/podman:v4.3.1
-  variables:
-    CI_REGISTRY_IMAGE: quay.io/shivering-isles/kos
-  before_script:
-    - podman login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-  script:
-    - . images/kos/.release
-      export release
-    - podman build --pull
-      --label "org.opencontainers.image.source=$CI_PROJECT_URL/-/tree/$CI_COMMIT_SHA/images/kos"
-      --label "org.opencontainers.image.revision=$CI_COMMIT_SHA"
-      --label "org.opencontainers.image.title=kOS"
-      -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
-      --format docker
-      images/kos
-    - podman push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA"
-    - podman push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-$CI_COMMIT_SHORT_SHA" "$CI_REGISTRY_IMAGE:${release}"
-  rules:
-    - if: '$CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH && $CI_PIPELINE_SOURCE == "push"'
-      changes:
-        paths:
-          - images/kos/**/*
-  tags:
-    - hetzner    
\ No newline at end of file