Add workflow to push image

This is so far some copy&paste work from OpenProject.
Might need further cleanup of duplication.

Author: NobodysNightmare

.github/workflows/release-image.yml

@@ -0,0 +1,101 @@
+name: Release image
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read # to fetch code (actions/checkout)
+
+env:
+  REGISTRY_IMAGE: openproject/keycloak-openproject-id
+  KEYCLOAK_VERSION: 26.3.3
+
+jobs:
+  build:
+    if: github.repository == 'opf/openproject-id'
+    needs:
+      - setup
+    runs-on:
+      labels: "runs-on=${{ github.run_id }}/ssh=false/${{ matrix.runner }}"
+    strategy:
+      matrix:
+        include:
+          - platform: linux/amd64
+            digest: amd64
+            runner: runner=4cpu-linux-x64
+          - platform: linux/arm64/v8
+            digest: arm64
+            runner: runner=4cpu-linux-arm64
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+      - name: Build image
+        id: build
+        uses: docker/build-push-action@v6
+        with:
+          context: image
+          file: image/Containerfile
+          platforms: ${{ matrix.platform }}
+          build-args: |
+            BUILDKIT_PROGRESS=plain
+          pull: true
+          load: true
+          tags: ${{ env.KEYCLOAK_VERSION }}
+          cache-from: type=s3,blobs_prefix=cache/${{ github.repository }}/,manifests_prefix=cache/${{ github.repository }}/,region=${{ env.RUNS_ON_AWS_REGION }},bucket=${{ env.RUNS_ON_S3_BUCKET_CACHE }}
+          cache-to: type=s3,blobs_prefix=cache/${{ github.repository }}/,manifests_prefix=cache/${{ github.repository }}/,region=${{ env.RUNS_ON_AWS_REGION }},bucket=${{ env.RUNS_ON_S3_BUCKET_CACHE }},mode=max
+      - name: Push image
+        id: push
+        uses: docker/build-push-action@v6
+        with:
+          context: image
+          file: image/Containerfile
+          platforms: ${{ matrix.platform }}
+          build-args: |
+            BUILDKIT_PROGRESS=plain
+          outputs: type=image,name=${{ env.REGISTRY_IMAGE }},push-by-digest=true,name-canonical=true,push=true
+          cache-from: type=s3,blobs_prefix=cache/${{ github.repository }}/,manifests_prefix=cache/${{ github.repository }}/,region=${{ env.RUNS_ON_AWS_REGION }},bucket=${{ env.RUNS_ON_S3_BUCKET_CACHE }}
+          cache-to: type=s3,blobs_prefix=cache/${{ github.repository }}/,manifests_prefix=cache/${{ github.repository }}/,region=${{ env.RUNS_ON_AWS_REGION }},bucket=${{ env.RUNS_ON_S3_BUCKET_CACHE }},mode=max
+  merge:
+    runs-on: ubuntu-latest
+    needs:
+      - setup
+      - build
+    steps:
+      - name: Merge digests
+        uses: actions/upload-artifact/merge@v4
+        with:
+          pattern: "digests-${{ inputs.tag }}-${{ matrix.digest }}*"
+          overwrite: true
+          name: "merged-digests-${{ inputs.tag }}-${{ github.run_number }}-${{ github.run_attempt }}"
+      - name: Download digests
+        uses: actions/download-artifact@v5
+        with:
+          name: "merged-digests-${{ inputs.tag }}-${{ github.run_number }}-${{ github.run_attempt }}"
+          path: /tmp/digests
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.REGISTRY_IMAGE }}@sha256:%s ' *)
+      - name: Inspect image
+        run: |
+          docker buildx imagetools inspect ${{ env.REGISTRY_IMAGE }}:${{ env.KEYCLOAK_VERSION }}