Upgrade V2 API's to V3 API's

[sitaram-kalluri]

Which at_widget package you want to add enhancement?
at_onboarding_flutter

On what platforms do you want to add enhancement?
Android, iOS, Windows, MacOS, Linux

Is your feature request related to a problem?
At present, the onboarding widget communicates with the registrar API using V2 APIs. Upgrade to utilize V3 APIs.

[srieteja]

Code that interacts with RegistrarAPI on CLI side and Apps side is being consolidated into a single package which will be called "AtRegister". This package is almost ready and has code that has been upgraded to Registrar V3. When the package is published it needs to be consumed into RegisterCLI and OnboardingFlutter. @sachins-geekyants will be handling the onboarding_flutter side of things as discussed.
Issue link for AtRegister: #468

[sachins-geekyants]

@srieteja Let me know, If AtRegister can be used for testing in onboarding_flutter.

[srieteja]

@sachins-geekyants the AtRegister code is currently in #508. Feel free to take a look and try running the code, but I would recommend waiting till the PR is merged before you start integrating this with onboarding_flutter.

[srieteja]

Backloggin this until #508 is successfully merged.