How to add custom option screen before adding Dimensions and measures?

[Anonymous]

Hello Everyone, I am creating a custom extension where I can ask the user for input before calling the default method to add dimensions and measures. Something like this from one of the extensions I came across.

When I click on "Link to a chart" I should be able to call my custom function and when I click "Add Data" it should take the user to the default data selection options.

Does anyone know what exactly is the flow of control and when is this 'Add data' screen rendered?

Also, Is there a way I can programmatically invoke the "Add Data" screen?

Thanks in advance.