Add gitlab-ci.yml for CI/CD

.gitlab-ci.yml

+# Based on https://martin-renze.de/posts/gitlab-ci-releases/
+# https://docs.gitlab.com/ee/user/project/releases/release_cicd_examples.html
+# https://about.gitlab.com/blog/2023/11/01/tutorial-automated-release-and-release-notes-with-gitlab/
+stages:
+  - test
+  - prepare
+  - release
+
+phpcs:
+  stage: test
+  image: michaelmcandrew/civicrm-buildkit:latest
+  script:
+    - civilint
+    - phpcs-civi --ignore=vendor,docs --report-json=gl-code-quality-report-tmp.json --report-full=gl-fullreport.txt --report-junit=gl-report.xml . || true
+    - cat gl-fullreport.txt
+  artifacts:
+    reports:
+      codequality: gl-report.xml
+      junit: gl-report.xml
+
+release_notes:
+  stage: prepare
+  image: alpine:latest
+  rules:
+    - if: $CI_COMMIT_TAG
+  script:
+    - apk add curl jq
+    - 'curl -H "PRIVATE-TOKEN: $CI_API_TOKEN" "$CI_API_V4_URL/projects/$CI_PROJECT_ID/repository/changelog?version=$CI_COMMIT_TAG" | jq -r .notes > release_notes.md'
+    - cat release_notes.md
+  artifacts:
+    paths:
+      - release_notes.md
+
+release_job:
+  stage: release
+  image: registry.gitlab.com/gitlab-org/release-cli:latest
+  needs:
+    - job: release_notes
+      artifacts: true
+  rules:
+    - if: $CI_COMMIT_TAG
+  script:
+    - echo "Running release_job for $TAG"
+  release:
+    name: 'Version $CI_COMMIT_TAG'
+    description: release_notes.md
+    tag_name: '$CI_COMMIT_TAG'
+    ref: '$CI_COMMIT_SHA'