Add "Docker Image CI" GHA Workflow

Pushing ...

1. `owntube/peertube-runner:v521`
2. `owntube/peertube-runner:v603`
3. `owntube/peertube-runner:latest` (alias of `v603`)

.github/workflows/docker-image-ci.yml

@@ -0,0 +1,31 @@
+name: Docker Image CI
+
+on:
+  push:
+    branches: [ "main" ]
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKER_HUB_USERNAME }}
+          password: ${{ secrets.DOCKER_HUB_TOKEN }}
+
+      - name: Build the `owntube/peertube-runner:v521` Docker image
+        run: docker build . --file Dockerfile.bullseye --tag owntube/peertube-runner:v521
+      - name: Test the `owntube/peertube-runner:v521` Docker image
+        run: docker run -it --rm --name v521-runner-help owntube/peertube-runner:v521 peertube-runner --help
+      - name: Push the `owntube/peertube-runner:v521` Docker image
+        run: docker push owntube/peertube-runner:v521
+
+      - name: Build the `owntube/peertube-runner:v603` Docker image
+        run: docker build . --file Dockerfile.bookworm --tag owntube/peertube-runner:v603
+      - name: Test the `owntube/peertube-runner:v603` Docker image
+        run: docker run -it --rm --name v603-runner-help owntube/peertube-runner:v603 peertube-runner --help
+      - name: Push the `owntube/peertube-runner:v603` Docker image
+        run: docker push owntube/peertube-runner:v603
+      - name: Push the `owntube/peertube-runner:latest` Docker image
+        run: docker tag owntube/peertube-runner:v603 owntube/peertube-runner:latest && docker push owntube/peertube-runner:latest