Add validation logic for init flags

### 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