fix(GODT-3124): Handling of sync child jobs

Improve the handling of sync child jobs to ensure it behaves correctly
in all scenarios.

The sync service now uses a isolated context to avoid all the pipeline
stages shutting down before all the sync tasks have had the opportunity
to run their course.

The job waiter now immediately starts with a counter of 1 and waits
until all the child and the parent job finish before considering the
work to be finished.

Finally, we also handle the case where a sync job can't be queued
because the calling context has been cancelled.

internal/services/syncservice/interfaces.go

@@ -64,7 +64,7 @@ func (s Status) InProgress() bool {
 
 // Regulator is an abstraction for the sync service, since it regulates the number of concurrent sync activities.
 type Regulator interface {
-	Sync(ctx context.Context, stage *Job)
+	Sync(ctx context.Context, stage *Job) error
 }
 
 type BuildResult struct {