add github actions for dockerhub push

.github/workflows/dockerhub.yaml

@@ -0,0 +1,38 @@
+name: Publish image to Docker Hub
+
+on:
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - '**.md'
+      - '.gitignore'
+      - '.github'
+
+jobs:
+  push_to_registry:
+    name: Push Docker image to Docker Hub
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ryojpn
+          password: ${{ secrets.DOCKER_PASSWORD }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ryojpn/nutrition-api
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}