Refactor NormativaService to use axios and improve error handling; enhance OnboardingView for normativa fetching

- Updated NormativaService to utilize axios for API requests, replacing the previous apiClient.
- Changed the method from an object to a static class method for better structure.
- Improved error handling in NormativaService to return null on failure.
- Refactored OnboardingView to streamline normativa fetching with enhanced error handling and loading state management.
- Added clearer comments and improved code structure for better maintainability.