allow passing empty scheduled actions

[cluarkhpe]

the following code to create a service will fail with an error saying that scheduled actions must be specified:

_, err = pagerdutyClient.CreateServiceWithContext(context.Background(), pagerduty.Service{
                Name:             "testlibfailservice",
                Description:      "for testing lib failures",
                EscalationPolicy: *escalationPolicy,
                AlertCreation:    "create_alerts_and_incidents",
                IncidentUrgencyRule: &pagerduty.IncidentUrgencyRule{
                        Type:    "use_support_hours",
                        Urgency: "severity_based",
                        DuringSupportHours: &pagerduty.IncidentUrgencyType{
                                Type:    "constant",
                                Urgency: "high",
                        },
                        OutsideSupportHours: &pagerduty.IncidentUrgencyType{
                                Type:    "constant",
                                Urgency: "low",
                        },
                },
                SupportHours: &pagerduty.SupportHours{
                        Type:       "fixed_time_per_day",
                        Timezone:   "America/Lima",
                        StartTime:  "09:00:00",
                        EndTime:    "17:00:00",
                        DaysOfWeek: []uint{1, 2, 3, 4, 5},
                },
                ScheduledActions: []pagerduty.ScheduledAction{},
        })

a direct call to the api with the same inputs works
curl -X POST --data "@service.json" -H "Authorization: Token token=$PAGERDUTY_TOKEN" -H "Content-Type: application/json" https://api.pagerduty.com/services
service.json:

{
  "service": {
    "name": "testapifailservice",
    "description": "for testing api",
    "alert_creation": "create_alerts_and_incidents",
    "scheduled_actions": [],
    "support_hours": {
      "type": "fixed_time_per_day",
      "time_zone": "America/Lima",
      "days_of_week": [
        1,
        2,
        3,
        4,
        5
      ],
      "start_time": "09:00:00",
      "end_time": "17:00:00"
    },
    "escalation_policy": {
      "id": "<ESCALATION_POLICY_ID>",
      "type": "escalation_policy_reference"
    },
    "incident_urgency_rule": {
      "type": "use_support_hours",
      "during_support_hours": {
        "type": "constant",
        "urgency": "high"
      },
      "outside_support_hours": {
        "type": "constant",
        "urgency": "low"
      }
    },
    "type": "service"
  }
}