Add Docker Hub login step to CI workflow

Author: seaniiio

.github/workflows/loadtest-cd.yml

@@ -103,6 +103,12 @@ jobs:
           KOREA_TOURISM_API_KEY=${{ secrets.KOREA_TOURISM_API_KEY }}
           ENVEOF
 
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Pull latest image
         run: docker pull ${{ env.DOCKER_IMAGE_REPO }}:${{ env.IMAGE_TAG }}