In-app identification when API is throttling requests

[lszinv]

Currently, the app is unable to identify when the migration is processing and when it is waiting between throttling times.
An additional set of changes would be needed to fix this, including

• Submitting a change to the Tableau Migration SDK to raise an event, or call a hook upon identifying this scenario
• Consuming it in the app and displaying appropriate visual feedback on the remaining wait time.