Use source generation to create the `public partial class Program` needed by UITT (OSOE-829)

[sarahelsaig]

Now that we are dabbling in source generators, should we replace the boilerplate

[SuppressMessage(
    "Design",
    "CA1050: Declare types in namespaces",
    Justification = "As described here: https://docs.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-6.0.")]
public partial class Program
{
    protected Program()
    {
        // Nothing to do here.
    }
}

with generated source too?

Jira issue