[enhancement] Same Autosuspend Calendar for many hosts

[isaaclw]

It would be nice if there was a configuration option for the wakeup caledar (and the active calendar?), where it only processed events with a certain message in them.

Then you could re-use the calendar for other things, including other servers.

For example, I would put something in the config like this:

[wakeup.Calendar]
enabled = true   
url = https://calendar.google.com/...
summary_match = 'wakeup: hertz'

And then I would put 'wakeup: hertz' on the calendar, and it would only wakeup on calendar events with that message

[languitar]

Sounds like a reasonable request. I'll see what I can do. Or if you know Python, a PR is also very welcome.