Extend monitoring by tedge-watchdog to third-party tedge extensions

[albinsuresh]

Extend monitoring by tedge-watchdog to any third-party tedge extension service that honours the tedge health-check contract by sending its health status to tedge/health/<service-name> when prompted with a health check request on tedge/health-check/<service-name>. The tedge-watchdog can provide a configuration file that lets users to configure the processes that they'd like it to monitor, in addition to the other tedge daemons.