API return 404 when a pre-enrollment already exists

[BryanttV]

Description

When a pre-enrollment already exists the API returns a 404 status code. This code is not the most appropriate. It should be a 400 status code.

Originally posted by @mariajgrimaldi in #289 (comment)

Possible Solution

The NotFound class by default has this status code:

eox-core/eox_core/edxapp_wrapper/backends/pre_enrollment_l_v1.py

Line 45 in 7f13278

raise NotFound(f'Pre-enrollment already exists for email: {email} course_id: {course_id}') from IntegrityError

Maybe using the ValidationError class (400) in this case is better.