fix: ninja controller and view

[ruilopesm]

No description provided.

[reviewpad]

AI-Generated Summary: This pull request includes changes to multiple files where the NinjaView was replaced with NinjaJSON. Modifications were done in 'ninja_json.ex', 'auth_view.ex', 'enrollment_view.ex' and 'lecture_view.ex' files. Additionally, the entire file, 'ninja_view.ex', was deleted, which had functions to render JSON views for the 'ninja' model. Several adjustments are made to the 'NinjaJSON' module, including adding the 'Ninja' alias, renaming the function 'guardian_attrs' to 'guardian', and modifying the structure of the data function. The pull request consists of 10 insertions and 68 deletions which overall simplifies the project structure by eliminating the redundant 'NinjaView' module.