Mapping is not cleaned up in database when service is removed from PagerDuty

[aladjadj]

Describe the bug
If a service is deleted or recreated on PagerDuty side, the mapping was not cleaned up

To Reproduce
Steps to reproduce the behavior:

1. Create a service in PagerDuty
2. Create a service in Backstage (Without pagerduty annotation)
3. Map the service in backstage instance /pagerduty
4. The service is Sync and the Backstage service has new pagerduty annotations
   -> At this step all good <-
5. Delete the service in the PagerDuty
6. Re-create the service in the PagerDuty (with new ID)
7. The new PagerDuty service is available in /pagerduty but it is impossible to map the Backstage Service again.

Expected behavior

• The service from backstage (mapped to old pagerduty service) should be available to re-assign to new service.
• Add the capability to delete existing mapping

Screenshots