executors PeriodicalExecutor can support add workers

[munding]

A periodic executor performing I/O operations like HTTP reporting can easily cause data accumulation. Adding an option to set the number of workers during the creation of a new PeriodicalExecutor can help.

周期性 Executor 在执行一些 io 操作，比如 http 上报，很容易造成数据堆积，在 New PeriodicalExecutor 的过程中可以选择添加 worker 数量的选项

[kevwan]

You can decide how to run tasks, because TaskContainer interface let you write your own execution logic.

	// TaskContainer interface defines a type that can be used as the underlying
	// container that used to do periodical executions.
	TaskContainer interface {
		// AddTask adds the task into the container.
		// Returns true if the container needs to be flushed after the addition.
		AddTask(task any) bool
		// Execute handles the collected tasks by the container when flushing.
		Execute(tasks any)
		// RemoveAll removes the contained tasks, and return them.
		RemoveAll() any
	}