support rk-boot reload config on sighup or watch config

[katevi]

Hello! I am wondering if rk-boot supports updating boot.yaml config on the fly.
It would be convenient in case we wanted to change the logging level of a component on the fly, for example.
It seems similar configuration tool Viper already has watching configs

[dongxuny]

@katevi Hi, in the current implementation, watching boot.yaml with reloading is not supported. However, I do think it is a good features for rk-boot.

I will implement the reloading logic in the next rk-xxx release.

Thanks