Customizable API Error Responses

[SandeepLakka]

Is your feature request related to a problem? Please describe.
Mockify currently always returns valid data, but users may want to simulate API errors (e.g., 404, 500, etc.).

Describe the solution you'd like
Allow users to define custom API error responses, including:

HTTP status codes like 400, 404, 500, etc.

Custom error messages based on different conditions.

Describe alternatives you've considered
Manually simulating errors by modifying API logic.

Additional context
This feature will help users simulate a wide range of real-world API responses.