Add job monitor interface to allow for collecting job metrics (#659)

* Add metrics each run of job

* Fix lint

* Fix test lint

* Fix backwards job status

* Add tags

* Comment example

* Rename it

* Fix some names

* Fix readme

* update readme, examples, naming

* fix unrelated test that was leaking scheduler

* remove overzealous leak detection

* rename interface methods

---------

Co-authored-by: gorodet-sky <gorodetsky.dev@gmail.com>

example_test.go

@@ -684,6 +684,69 @@ func ExampleWithLogger() {
 	)
 }
 
+func ExampleWithMonitor() {
+	//type exampleMonitor struct {
+	//	mu      sync.Mutex
+	//	counter map[string]int
+	//	time    map[string][]time.Duration
+	//}
+	//
+	//func newExampleMonitor() *exampleMonitor {
+	//	return &exampleMonitor{
+	//	counter: make(map[string]int),
+	//	time:    make(map[string][]time.Duration),
+	//}
+	//}
+	//
+	//func (t *exampleMonitor) IncrementJob(_ uuid.UUID, name string, _ []string, _ JobStatus) {
+	//	t.mu.Lock()
+	//	defer t.mu.Unlock()
+	//	_, ok := t.counter[name]
+	//	if !ok {
+	//		t.counter[name] = 0
+	//	}
+	//	t.counter[name]++
+	//}
+	//
+	//func (t *exampleMonitor) RecordJobTiming(startTime, endTime time.Time, _ uuid.UUID, name string, _ []string) {
+	//	t.mu.Lock()
+	//	defer t.mu.Unlock()
+	//	_, ok := t.time[name]
+	//	if !ok {
+	//		t.time[name] = make([]time.Duration, 0)
+	//	}
+	//	t.time[name] = append(t.time[name], endTime.Sub(startTime))
+	//}
+	//
+	//monitor := newExampleMonitor()
+	//s, _ := NewScheduler(
+	//	WithMonitor(monitor),
+	//)
+	//name := "example"
+	//_, _ = s.NewJob(
+	//	DurationJob(
+	//		time.Second,
+	//	),
+	//	NewTask(
+	//		func() {
+	//			time.Sleep(1 * time.Second)
+	//		},
+	//	),
+	//	WithName(name),
+	//	WithStartAt(
+	//		WithStartImmediately(),
+	//	),
+	//)
+	//s.Start()
+	//time.Sleep(5 * time.Second)
+	//_ = s.Shutdown()
+	//
+	//fmt.Printf("Job %q total execute count: %d\n", name, monitor.counter[name])
+	//for i, val := range monitor.time[name] {
+	//	fmt.Printf("Job %q execute #%d elapsed %.4f seconds\n", name, i+1, val.Seconds())
+	//}
+}
+
 func ExampleWithName() {
 	s, _ := NewScheduler()
 	defer func() { _ = s.Shutdown() }()