add docker workflow using docker hub as remote

.github/workflows/docker.yml

@@ -0,0 +1,24 @@
+name: Build Docker image
+on:
+    push:
+        branches:
+            - main
+jobs:
+    docker:
+        runs-on: ubuntu-latest
+        steps:
+            - name: Set up Docker buildx
+              uses: docker/setup-buildx-action@v3
+            - name: Log in to container registry
+              uses: docker/login-action@v3
+              with:
+                  username: openwf
+                  password: ${{ secrets.DOCKERHUB_TOKEN }}
+            - name: Build and push
+              uses: docker/build-push-action@v6
+              with:
+                  platforms: linux/amd64,linux/arm64
+                  push: true
+                  tags: |
+                      openwf/spaceninjaserver:latest
+                      openwf/spaceninjaserver:${{ github.sha }}