[Signals] Options/Params to disable signal handling #199

Is your feature request related to a problem? Please describe.
The problem is, that when running the server processes manually even with & or nohup the processes end when ssh session is closed.
(no docker available on embedded / router).

I expect this is the source:
https://github.com/rustdesk/rustdesk-server/blob/master/src/common.rs#L154

Describe the solution you'd like
Would be good to have the option to disable specific signal handlers or all, by env vars or commandline arguments.

Describe alternatives you've considered
I tried nohup without luck and the only alternative might be to have a wrapper that blocks these signals for child processes.

https://stackoverflow.com/questions/4515274/externally-disabling-signals-for-a-linux-program
rust-lang/rust#100737

Might be possible with pthread_sigmask somehow.

Currently I use a workaround using the crontab that works but is not ideal.

Additional context
Add any other context about the feature request here.