Test Data: Fixing endpoint not working #20044 (#20227)

* It worked before i must have broken it somehow. Commit as checkpoint

* Adding a reference from Web.UI.csproj to TestData to allow composers to be composed

* Changing readme and removing project reference

tests/Umbraco.TestData/TestDataComposer.cs

@@ -0,0 +1,10 @@
+using Umbraco.Cms.Core.Composing;
+using Umbraco.Cms.Core.DependencyInjection;
+using Umbraco.TestData.Extensions;
+
+namespace Umbraco.TestData;
+
+public class TestDataComposer : IComposer
+{
+    public void Compose(IUmbracoBuilder builder) => builder.AddUmbracoTestData();
+}