Integrate conductor graceful shutdown and drain functionality into ironic-operator lifecycle management

Description:

After backporting conductor graceful shutdown and drain capabilities from upstream Ironic, integrate these features into the ironic-operator to ensure conductor pods shutdown gracefully without interrupting in-progress operations.

Acceptance Criteria:

• Implement <something> in IronicConductor pod spec that triggers conductor drain before shutdown.
  • preStop hook ?
  • Just always use SIGUSR2 ?
• Configure appropriate terminationGracePeriodSeconds to allow in-progress tasks to complete
• Update IronicConductor controller to monitor drain status before terminating pods
• Implement readiness probe that accounts for conductor drain state (mark not-ready when draining)
• Configure StatefulSet rolling update strategy to respect drain lifecycle
• Add status fields to IronicConductor CR to track drain state per conductor pod

Nice to have, may want to break these out as separate stories:

• Verify rolling updates wait for drain completion before terminating conductor pods
• Test graceful shutdown with long-running operations (e.g., node deployment, cleaning)

Technical Context:

• Controller: `controllers/ironicconductor_controller.go`
• Affects: IronicConductor StatefulSet configuration
• Pod lifecycle: preStop hooks?, terminationGracePeriodSeconds
• Probes: readiness/liveness probe configuration
• Status tracking: Add drain state to IronicConductor CR status
• Dependencies: Requires OSPRH-22299  (backported graceful shutdown code) to be complete