Add docker snapshot workflow

.gitea/workflows/docker-snapshot.yaml

@@ -0,0 +1,26 @@
+name: Build and publish docker image snapshot
+run-name: ${{ gitea.actor }} runs ci pipeline
+on: [ push ]
+
+jobs:
+  build-and-publish:
+    runs-on: ubuntu-latest
+    if: gitea.ref == 'refs/heads/master'
+    steps:
+      - uses: https://github.com/actions/checkout@v4
+      - name: Set up Docker Buildx
+        uses: https://github.com/docker/setup-buildx-action@v3
+      - name: Login to Gitea Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: gitea.forstenlechner.dev
+          username: stefan
+          password: ${{ secrets.ACTION_TOKEN }}
+      - name: Build and push Docker image
+        uses: https://github.com/docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: |
+            gitea.forstenlechner.dev/stefan/simple-picture-gallery:${{gitea.sha}}
+            gitea.forstenlechner.dev/stefan/simple-picture-gallery:latest