ci: Build docker image

Signed-off-by: Julius Härtl <jus@bitgrid.net>

.github/workflows/docker.yml

@@ -0,0 +1,87 @@
+name: Docker image
+
+on:
+  push:
+    branches:
+        - ci/docker
+        - main
+        - master
+        - stable*
+    tags:
+      - "v*"
+
+env:
+  # DOCKER_REPO: nextcloud/whiteboard
+  GHCR_REPO: ghcr.io/nextcloud/whiteboard
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    strategy:
+      matrix:
+        platform:
+          - linux/amd64
+          - linux/arm64
+          - linux/arm/v5
+          - linux/arm/v7
+
+    steps:
+      - name: Set vars
+        id: vars
+        run: |
+          echo "version=${GITHUB_REF#refs/tags/v}" >> $GITHUB_OUTPUT
+          echo "platform=$(echo -n ${{ matrix.platform }} | sed 's/\//-/g')" >> $GITHUB_OUTPUT
+
+      - uses: actions/checkout@v3
+      - uses: docker/setup-qemu-action@v3
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Login to Github Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build docker images
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          push: true
+          platforms: ${{ matrix.platform }}
+          tags: |
+            ${{ env.GHCR_REPO}}:${{ steps.vars.outputs.version }}-${{ steps.vars.outputs.platform }}
+
+  release:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    needs: build
+
+    steps:
+      - name: Set vars
+        id: vars
+        run: |
+          echo "version=${GITHUB_REF#refs/tags/v}" >> $GITHUB_OUTPUT
+          echo "version=daily" >> $GITHUB_OUTPUT
+
+      - name: Login to Github Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Create GHCR manifest
+        run: |
+          docker manifest create $GHCR_REPO:${{ steps.vars.outputs.version }} \
+            $GHCR_REPO:${{ steps.vars.outputs.version }}-linux-amd64 \
+            $GHCR_REPO:${{ steps.vars.outputs.version }}-linux-arm64 \
+            $GHCR_REPO:${{ steps.vars.outputs.version }}-linux-arm-v5 \
+            $GHCR_REPO:${{ steps.vars.outputs.version }}-linux-arm-v7
+
+      - name: Push manifests
+        run: |
+          docker manifest push $DOCKER_REPO:${{ steps.vars.outputs.version }}
+          docker manifest push $GHCR_REPO:${{ steps.vars.outputs.version }}