fix(ci): cache ubuntu-24.04 cloud image on runner, pass to bm-bootstrap

Add a step before the E2E run that ensures the Ubuntu 24.04 noble cloud
image is cached at BM_ISO_CACHE. Downloads from ubuntu.com if missing,
prints cached size if present. Passes path via BM_UBUNTU_IMAGE to
bm-bootstrap.sh which SCPs it to the node for --file import.

.github/workflows/e2e-baremetal.yml

@@ -79,11 +79,24 @@ jobs:
           EPDU_SNMP_PRIV_PASS=${{ secrets.BM_EPDU_PRIV_PASS }}
           EOF
 
+      - name: Cache Ubuntu 24.04 cloud image
+        run: |
+          IMG="${BM_ISO_CACHE}/ubuntu-24.04-cloudimg-amd64.img"
+          if [ ! -f "$IMG" ]; then
+            echo "Downloading Ubuntu 24.04 cloud image..."
+            sudo curl -fsSL -o "$IMG" \
+              "https://cloud-images.ubuntu.com/noble/current/noble-server-cloudimg-amd64.img"
+            echo "  Downloaded $(du -h "$IMG" | cut -f1)"
+          else
+            echo "Ubuntu 24.04 cloud image cached ($(du -h "$IMG" | cut -f1))"
+          fi
+
       - name: Run Bare-Metal E2E
         env:
           BM_CI_PASSWORD: ${{ secrets.BM_CI_PASSWORD }}
           BM_SSH_KEY: ${{ runner.temp }}/bm-ci
           BM_EPDU_ENV: ${{ runner.temp }}/epdu.env
+          BM_UBUNTU_IMAGE: ${{ env.BM_ISO_CACHE }}/ubuntu-24.04-cloudimg-amd64.img
           SPX_EXTERNAL_POOL: ${{ env.SPINIFEX_CI_POOL }}
         run: |
           sudo -E mulga/scripts/baremetal/run-baremetal-e2e.sh \