Make global timer configureable

[swimmesberger]

First off - thanks for creating a lightweight scheduling library!

Describe the solution you'd like
The scheduling use-cases can vary on a project-to-project basis.
Some project require precision in the seconds/minutes; some require only precision in hours/days.
For those "simple" daily cases running the timer every second* seems wasteful so it would be nice to be able to configure the global timer.
*https://github.com/jamesmh/coravel/blob/master/Src/Coravel/Scheduling/HostedService/SchedulerHost.cs#L40