gha: publish docker image only on pushes to branch server

.github/workflows/on-push-server.yaml

@@ -0,0 +1,42 @@
+name: On Push Server
+
+on:
+  push:
+    branches:
+      - server
+
+jobs:
+  push-docker-image:
+    runs-on: ubuntu-latest
+    env:
+      DOCKER_CLI_EXPERIMENTAL: "enabled"
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: tag
+        id: next_tag
+        run: echo "tag=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v2
+        with:
+          install: true
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build & push prem
+        run:  >-
+          docker buildx build --push
+          --file Dockerfile
+          --tag ghcr.io/premai-io/prem-app:latest
+          --platform linux/arm64,linux/amd64 .