add image build gh action

.github/workflows/build-image.yaml

@@ -0,0 +1,43 @@
+name: Build image and push to ghcr.io
+
+on:
+  push:
+    branches:
+      - master
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: kennhung/aws-prometheus-updater
+
+jobs:
+  build-image:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=sha,enable=true,prefix=sha-,suffix=,format=short
+      - name: Build and push Docker image
+        id: push
+        uses: docker/build-push-action@v5
+        with:
+          context: ${{ matrix.target }}
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max