V14: Fix member mapping (#16106)

* convert key to name before saving roles

* Rework MemberEditingService to convert keys

* Rename variable to groups

* Extract to variable

src/Umbraco.Core/Models/ContentEditing/MemberEditingModelBase.cs

@@ -4,7 +4,7 @@ public abstract class MemberEditingModelBase : ContentEditingModelBase
 {
     public bool IsApproved { get; set; }
 
-    public IEnumerable<string>? Roles { get; set; }
+    public IEnumerable<Guid>? Roles { get; set; }
 
     public string Email { get; set; } = string.Empty;