add docker workflow

.github/workflows/docker.yml

@@ -0,0 +1,31 @@
+name: Docker main build
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+concurrency:
+  group: docker-main
+  cancel-in-progress: true
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build the new image
+        run: docker build . -t ghcr.io/zeuswpi/haldis:${{ github.sha }}
+      - name: Tag the new image with latest
+        run: docker tag ghcr.io/zeuswpi/haldis:${{ github.sha }} ghcr.io/zeuswpi/haldis:latest
+      - name: Push Docker image
+        run: docker push --all-tags ghcr.io/zeuswpi/haldis