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

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

tests/Umbraco.Tests.Integration/Testing/UmbracoIntegrationTestWithContent.cs

@@ -35,7 +35,7 @@ public abstract class UmbracoIntegrationTestWithContent : UmbracoIntegrationTest
     protected ContentType ContentType { get; private set; }
 
     [SetUp]
-    public void Setup() => CreateTestData();
+    public virtual void Setup() => CreateTestData();
 
     public virtual void CreateTestData()
     {