feat: Added workflow for backend.

Author: kash2104

.github/workflows/backend.yml

@@ -0,0 +1,32 @@
+name: Build backend docker images
+
+on:
+  push:
+    paths:
+      - "Server/**"
+
+jobs:
+  build-image:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Docker hub login
+        uses: docker/login-action@v3
+        with:
+          username: ${{secrets.DOCKERHUB_USERNAME}}
+          password: ${{secrets.DOCKERHUB_PASSWORD}}
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up docker buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Backend image
+        uses: docker/build-push-action@v6
+        with:
+          context: ./Server
+          push: true
+          tags: ${{secrets.DOCKERHUB_USERNAME}}/uniprep-backend:latest