Improve the doc of Microsoft.Extensions.Configuration.Configurationbinder.Getvalue

Need to clarify the behavior of the extension methods [`IConfiguration.GetValue](https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.configuration.configurationbinder.getvalue?view=net-8.0#microsoft-extensions-configuration-configurationbinder-getvalue-1(microsoft-extensions-configuration-iconfiguration-system-string)) to explain how these API read the configuration and convert it to type. It is worth explaining how these APIs differ than other configuration binding APIs. Look at the issue https://github.com/dotnet/runtime/issues/103418 for more discussions around that.