Initialize important services before unattended installs (#17366)

* Added new notification to hook in after the premigrations and use this to init different services.

* Force MaxDegreeOfParallelism to 1, while investigating scopes

* Tried some more workarounds

* Updated scopes and changed parallel to non parallel to ensure migration works

* Missing scope

* Make it parallel again - The secret is, the SuppressFlow needs to be when you create the task, but not on the await!.

* Fixed issue when DEBUG_SCOPES is not added to tests.

* Remove test exception

* Try build on ubuntu again, even that we know it can be stuck. Just a test to see if all tests pass

* Updated comment

---------

Co-authored-by: kjac <kja@umbraco.dk>

src/Umbraco.PublishedCache.HybridCache/NotificationHandlers/SeedingNotificationHandler.cs

@@ -32,9 +32,7 @@ internal class SeedingNotificationHandler : INotificationAsyncHandler<UmbracoApp
             return;
         }
 
-        await Task.WhenAll(
-            _documentCacheService.SeedAsync(cancellationToken),
-            _mediaCacheService.SeedAsync(cancellationToken)
-        );
+        await _documentCacheService.SeedAsync(cancellationToken);
+        await _mediaCacheService.SeedAsync(cancellationToken);
     }
 }