Add container.FilterSlice function (#30339)

Many places have the following logic:
```go
func (jobs ActionJobList) GetRunIDs() []int64 {
	ids := make(container.Set[int64], len(jobs))
	for _, j := range jobs {
		if j.RunID == 0 {
			continue
		}
		ids.Add(j.RunID)
	}
	return ids.Values()
}
```

this introduces a `container.FilterMapUnique` function, which reduces
the code above to:
```go
func (jobs ActionJobList) GetRunIDs() []int64 {
	return container.FilterMapUnique(jobs, func(j *ActionRunJob) (int64, bool) {
		return j.RunID, j.RunID != 0
	})
}
```

models/actions/schedule_list.go

@@ -18,19 +18,15 @@ type ScheduleList []*ActionSchedule
 
 // GetUserIDs returns a slice of user's id
 func (schedules ScheduleList) GetUserIDs() []int64 {
-	ids := make(container.Set[int64], len(schedules))
-	for _, schedule := range schedules {
-		ids.Add(schedule.TriggerUserID)
-	}
-	return ids.Values()
+	return container.FilterSlice(schedules, func(schedule *ActionSchedule) (int64, bool) {
+		return schedule.TriggerUserID, true
+	})
 }
 
 func (schedules ScheduleList) GetRepoIDs() []int64 {
-	ids := make(container.Set[int64], len(schedules))
-	for _, schedule := range schedules {
-		ids.Add(schedule.RepoID)
-	}
-	return ids.Values()
+	return container.FilterSlice(schedules, func(schedule *ActionSchedule) (int64, bool) {
+		return schedule.RepoID, true
+	})
 }
 
 func (schedules ScheduleList) LoadTriggerUser(ctx context.Context) error {