Enable multiple pages in server stub code for ToDo app

[lirenhe]

In current implementation, we only support return one page in the stub code.
We could maintain 2 items in the returned list and one item in each page.

typespec-e2e-demo/todoApp/servers/aspnet/impl/AttachmentsOperations.cs

Line 60 in f7e6206

public async Task<PageTodoAttachment> ListAsync(long itemId)

[lirenhe]

Let's postpone this effort to see how stub code generation could help in this area.