CloudMigrations: Omit autoincremented id for alert snapshots (#106598)

If you tried to migrate alerts from two differente sources/on-prem instances,
the autoincremented numeric id would be the same, and since we were creating
the resource in cloud with that same id (the API accepts it), it would
return an error "conflicting alert rule found" because that id is the primary key on the table.

We simply omit the numeric id now and let the API for the cloud instance generate it.

pkg/services/cloudmigration/cloudmigrationimpl/snapshot_mgmt_alerts.go

@@ -135,7 +135,6 @@ type alertRule struct {
 	Title                string                                     `json:"title"`
 	ExecErrState         string                                     `json:"execErrState"`
 	Data                 []definitions.AlertQuery                   `json:"data"`
-	ID                   int64                                      `json:"id"`
 	For                  model.Duration                             `json:"for"`
 	OrgID                int64                                      `json:"orgID"`
 	IsPaused             bool                                       `json:"isPaused"`
@@ -158,7 +157,6 @@ func (s *Service) getAlertRules(ctx context.Context, signedInUser *user.SignedIn
 		}
 
 		provisionedAlertRules = append(provisionedAlertRules, alertRule{
-			ID:                   rule.ID,
 			UID:                  rule.UID,
 			OrgID:                rule.OrgID,
 			FolderUID:            rule.NamespaceUID,
@@ -208,7 +206,6 @@ func (s *Service) getAlertRuleGroups(ctx context.Context, signedInUser *user.Sig
 			}
 
 			provisionedAlertRules = append(provisionedAlertRules, alertRule{
-				ID:                   rule.ID,
 				UID:                  rule.UID,
 				OrgID:                rule.OrgID,
 				FolderUID:            rule.NamespaceUID,