[rfe] Notify a user when a rig is triggered

[TurboTurtle]

Right now the only indication a user has if a rig has been triggered is checking rig list and/or /var/log/rig/rig.log. This isn't exactly a great experience and I would like to see us providing an active notification.

My first thought is to optionally send an email. I haven't explored this too deeply though as I'm unsure of how complex we would have to make this functionality.

[juanmasg]

Basic email support should be easy to implement, however adding advanced features as authentication, send rate control to avoid spamming, etc might be more complicated.

A couple of ideas for this:

• Slack or Telegram (via python3-slacker or python3-pytelegrambotapi)
• journald / syslog