Refactor setting arrays to sets (#16058)

Co-authored-by: Bjarke Berg <mail@bergmania.dk>

src/Umbraco.Core/Configuration/Models/HelpPageSettings.cs

@@ -6,5 +6,5 @@ public class HelpPageSettings
     /// <summary>
     ///     Gets or sets the allowed addresses to retrieve data for the content dashboard.
     /// </summary>
-    public string[]? HelpPageUrlAllowList { get; set; }
+    public ISet<string> HelpPageUrlAllowList { get; set; } = new HashSet<string>();
 }