Fix null value for id field on inner nodes in MongoDB HotChocolate ex…

…ample

Related to ChilliCream#61

Add an `Id` field to the `Address` class in `misc/MongoDB/12.1/Person/Address.cs`.

* Add a new `Id` field of type `Guid` to the `Address` class.

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/ChilliCream/hotchocolate-examples/issues/61?shareId=XXXX-XXXX-XXXX-XXXX).

misc/MongoDB/12.1/Person/Address.cs

@@ -2,6 +2,7 @@ namespace Demo;
 
 public class Address
 {
+    public Guid Id { get; init; }
     public string Street { get; init; }
 
     public string City { get; init; }