fix: Make K8s staging deployment conditional on cluster availability

Make the staging deployment workflow conditional so it doesn't fail when
no Kubernetes cluster is configured.

Changes:
- Added conditional to deploy-helm job (only runs if KUBECONFIG exists)
- Added deployment-skipped job for when cluster is not available
- Both jobs provide informative PR comments

This allows the workflow to succeed even without a K8s cluster while
still building and pushing Docker images to GHCR.

Author: manavgup

.github/workflows/k8s-deploy-staging.yml

@@ -28,23 +28,6 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Free up disk space
-        run: |
-          echo "Disk space before cleanup:"
-          df -h
-
-          # Remove unnecessary packages and files
-          sudo rm -rf /usr/share/dotnet
-          sudo rm -rf /usr/local/lib/android
-          sudo rm -rf /opt/ghc
-          sudo rm -rf /opt/hostedtoolcache/CodeQL
-
-          # Clean docker system
-          docker system prune -af --volumes || true
-
-          echo "Disk space after cleanup:"
-          df -h
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3