OnceEvery is an object that will perform exactly one action every given interval.
NewOnceEvery creates a new OnceEvery struct
Do calls the function f if and only if Do hits the given periodic interval. In other words Do can be called multiple times during the interval but it gets called only once if it hits the interval tick. So if the interval is 10 seconds, and a total of 100 calls are made during this period, f will be called it every 10 seconds.