Add validation logic for init flags

[johnpc]

Is this feature request related to a new or existing Amplify category?

No response

Is this related to another service?

init

Describe the feature you'd like to request

if you make a typo in an amplify init flag, it takes until after cloudformation rolls back before you get any feedback on whether it did what you want or not.

Describe the solution you'd like

validation logic

Describe alternatives you've considered

n/a

Additional context

No response

Is this something that you'd be interested in working on?

• [ ] 👋 I may be able to implement this feature request

Would this feature include a breaking change?

• [ ] ⚠️ This feature might incur a breaking change