ci: add workflow

.github/workflows/docker-build-push.yml

@@ -0,0 +1,50 @@
+name: Build and Push Docker Image
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Extract Syncplay version from Dockerfile
+        id: get-version
+        run: |
+          syncplay_version=$(grep -oP '(?<=ENV SYNCPLAY=")[^"]+' Dockerfile)
+          echo "syncplay_version=${syncplay_version}"
+          echo "syncplay_version=${syncplay_version}" >> $GITHUB_OUTPUT
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to Docker Hub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64,linux/386,linux/arm/v7
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: |
+            ${{ secrets.DOCKER_IMAGE }}:v${{ steps.get-version.outputs.syncplay_version }}
+            ${{ secrets.DOCKER_IMAGE }}:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max