Deploy Docker Image with GitHub Actions (#5)

This PR adds automated Docker image deployment to CI.

### Test Plan

Deploy an image with CI:
https://github.com/cowprotocol/token-subgraph/actions/runs/4513583889/jobs/7948607289?pr=5

.github/workflows/deploy.yaml

@@ -0,0 +1,35 @@
+name: deploy
+on:
+  push:
+    branches: [main]
+    tags: [v*]
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ghcr.io/${{ github.repository }}
+          labels: |
+            org.opencontainers.image.licenses=MIT OR Apache-2.0
+      - uses: docker/build-push-action@v4
+        with:
+          context: server
+          file: server/Dockerfile
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}