Add automatic VM ID discovery via OpenNebula API

[metalgrid]

This PR introduces the following:

• Implements automatic VM ID discovery using an initContainer that queries the OpenNebula API
• Eliminates the need for manual VM configuration scripts (contrib/one-context.sh)

Changes Made

• New VM ID discovery service (vmid-discover/vmid-discover.py):
  • Queries OpenNebula API to find VM by node name
  • Writes VM ID to /var/lib/cloud/vm-id for CSI driver consumption
• Updated deployment manifests:
  • Added initContainer to nodeplugin DaemonSet for automatic VM ID discovery
  • Changed cloud directory from hostPath to emptyDir for better isolation
  • Added secret reference for OpenNebula API credentials

The motivation for this comes from our Talos-based kubernetes cluster that doesn't store the VM ID from the ONE context at boot.