Add job for building and publishing Docker image

.dockerignore

@@ -0,0 +1 @@
+Dockerfile

.github/workflows/ci.yml

@@ -84,4 +84,41 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: -- -D warnings
+          args: -- -D warnings
+
+  docker:
+    name: Build Docker image
+    runs-on: ubuntu-latest
+    concurrency:
+      group: docker
+      cancel-in-progress: true
+    if: success()
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+
+      - name: Login to ghcr.io
+        uses: docker/login-action@v2
+        if: github.ref == 'refs/heads/master'
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          file: Dockerfile
+          push: ${{ github.ref == 'refs/heads/master' }}
+          tags: |
+            ghcr.io/flatpak/flat-manager:${{ github.sha }}
+            ghcr.io/flatpak/flat-manager:latest
+          labels: |
+            org.opencontainers.image.revision=${{ github.sha }}
+            org.opencontainers.image.source=ssh://[email protected]:${{ github.repository }}.git
+            org.opencontainers.image.url=https://github.com/${{ github.repository }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max