Rework build process for SI-GitLab

Update base image, add `.gitlab-ci.yml`, integrate build process with
SI-GitLab features. All in all, getting a first image build ready to
use.

.gitlab-ci.yml

+image: quay.io/sheogorath/build-ah-engine
+
+before_script:
+  - podman login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
+stages:
+  - analyse
+  - build
+  - test
+  - tag
+  - deploy
+
+build:
+  stage: build
+  script:
+    - podman build --pull --build-arg "VCS_REF=$CI_COMMIT_SHA" --build-arg "BUILD_DATE=$(date --rfc-3339 ns)" -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - podman push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
+
+tagging-master:
+  stage: tag
+  script:
+    - podman pull "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
+    - si-tagging -l "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" "$CI_REGISTRY_IMAGE" "$(grep -e 'FROM docker.io/library/haproxy:' Dockerfile | sed -e 's/.*://' -e 's/-alpine$//')"
+    - podman images --format "{{.Repository}}:{{.Tag}}" "$CI_REGISTRY_IMAGE" | grep "$CI_REGISTRY_IMAGE" | xargs -L 1 podman push
+  only:
+    - master
+
+

Dockerfile

-ARG REPO=library
-FROM ${REPO}/haproxy:1.9-alpine
+FROM docker.io/library/haproxy:1.9.15-alpine
 
 EXPOSE 2375
 ENV ALLOW_RESTARTS=0 \
@@ -37,4 +36,4 @@ LABEL org.label-schema.schema-version="1.0" \
       org.label-schema.license=Apache-2.0 \
       org.label-schema.build-date="$BUILD_DATE" \
       org.label-schema.vcs-ref="$VCS_REF" \
-      org.label-schema.vcs-url="https://github.com/Tecnativa/docker-socket-proxy"
+      org.label-schema.vcs-url="https://git.shivering-isles.com/container-library/docker-socket-proxy"