update_and_reboot: make the reboot timeout configurable

The Reboot task in update_and_reboot relied on Ansible's built-in reboot_timeout of 600 seconds, which no consumer of the role could override.

This exposes it as update_and_reboot_task_reboot_timeout. The default stays at 600, so nothing changes for existing consumers.

Testing Farm's public ranch needs a higher value for bare metal guests, which power-cycle the whole platform on reboot. That override lives in testing-farm/infrastructure rather than here.

Resolves: TFT-5015

Generated-by: Claude Code