chore: add a GitHub workflow to just build images

Adding this to bypass sometimes flaky e2e tests (we'll work on these
too).

.github/workflows/build-core-image.yml

@@ -0,0 +1,39 @@
+name: Build core image
+
+on: [workflow_dispatch]
+
+jobs:
+  images:
+    runs-on: ubuntu-latest
+
+    needs: test
+    if: github.ref == 'refs/heads/develop'
+
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Setup Docker buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to the GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push container image to GitHub Container Registry
+        uses: docker/build-push-action@v5
+        with:
+          labels: |
+            org.opencontainers.image.revision=${{ github.sha }}
+          push: true
+          platforms: linux/amd64,linux/arm64
+          tags: |
+            ghcr.io/ar-io/ar-io-core:latest
+            ghcr.io/ar-io/ar-io-core:${{ github.sha }}