Adding watchdog feature

Fabfurrequested to merge
watchdog into main

To help avoiding situation like the one outlined in T400039 we can use the Systemd watchdog feature that automatically restarts the service if it stops sending updates at the pre-defined rate.

The feature must be enabled on systemd side (service unit) too, otherwise the application setup simply fails with a warning. The application will also notify Systemd when is up and running and when it's stopping (in order to avoid unexpected restarts).

The whole logic is under the configuration monitoring::enable_watchdog switch.

Bug: T400199

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