Add schedule's users as query param when listing open incidents associated to EP snashot

[imjaroiswebdev]

This update is meant to improve the open incidents list results that is shown when a Schedule is trying to be deleted, but It has open incidents associated with the Escalation Policy snapshot using the Schedule.

Test results

$ make testacc TESTARGS="-run TestAccPagerDutySchedule"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run TestAccPagerDutySchedule -timeout 120m
?       github.com/terraform-providers/terraform-provider-pagerduty     [no test files]
=== RUN   TestAccPagerDutySchedule_import
--- PASS: TestAccPagerDutySchedule_import (11.65s)
=== RUN   TestAccPagerDutySchedule_Basic
--- PASS: TestAccPagerDutySchedule_Basic (14.82s)
=== RUN   TestAccPagerDutyScheduleWithTeams_Basic
--- PASS: TestAccPagerDutyScheduleWithTeams_Basic (15.44s)
=== RUN   TestAccPagerDutySchedule_BasicWithExternalDestroyHandling
--- PASS: TestAccPagerDutySchedule_BasicWithExternalDestroyHandling (13.25s)
=== RUN   TestAccPagerDutyScheduleWithTeams_EscalationPolicyDependant
--- PASS: TestAccPagerDutyScheduleWithTeams_EscalationPolicyDependant (19.61s)
=== RUN   TestAccPagerDutyScheduleWithTeams_EscalationPolicyDependantWithOpenIncidents
--- PASS: TestAccPagerDutyScheduleWithTeams_EscalationPolicyDependantWithOpenIncidents (49.51s)
=== RUN   TestAccPagerDutySchedule_EscalationPolicyDependantWithOpenIncidents
--- PASS: TestAccPagerDutySchedule_EscalationPolicyDependantWithOpenIncidents (47.57s)
=== RUN   TestAccPagerDutyScheduleOverflow_Basic
--- PASS: TestAccPagerDutyScheduleOverflow_Basic (14.34s)
=== RUN   TestAccPagerDutySchedule_BasicWeek
--- PASS: TestAccPagerDutySchedule_BasicWeek (13.82s)
=== RUN   TestAccPagerDutySchedule_Multi
--- PASS: TestAccPagerDutySchedule_Multi (14.79s)
PASS
ok      github.com/terraform-providers/terraform-provider-pagerduty/pagerduty   215.461s