Backend/oxomi/cicd pipeline (#15)

## 📝작업 내용

- GitHub Actions 워크플로우(deploy.yml) 추가
- main 브랜치에 푸시될 때 자동으로 EC2 서버에 배포되도록 설정

Author: oxomi

.github/workflows/deploy.yml

@@ -0,0 +1,27 @@
+name: Deploy to EC2
+
+on:
+  push:
+    branches: [ "main" ]  # main 브랜치 푸시 시 실행
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Setup SSH
+        uses: webfactory/[email protected]
+        with:
+          ssh-private-key: ${{ secrets.EC2_SSH_KEY }}
+
+      - name: Deploy to EC2
+        run: |
+          ssh -o StrictHostKeyChecking=no ${{ secrets.EC2_USER }}@${{ secrets.EC2_HOST }} << 'EOF'
+            cd ~/ComTogether/backend
+            git pull
+            docker-compose down
+            docker-compose up --build -d
+          EOF