refactor: upgrade guardian controller to 1.7

[danielsp45]

No description provided.

[reviewpad]

AI-Generated Summary: This pull request contains a number of changes primarily aimed at refactoring and upgrading the guardian controller from 1.6 to 1.7. It involves modifications in four files with 17 insertions and 18 deletions.

The notable changes are following:

• In the UserController and GuardianController, BokkenWeb has been used with :controller instead of "1.6". This indicates an upgrade from version 1.6 to 1.7.
• The render function calls in UserController and GuardianController have been updated to use atom keys rather than string keys.
• The response header in GuardianController's create function is updated to use string interpolation instead of using Routes.guardian_path for location.
• The guardian_view.ex file has been renamed to guardian_json.ex and transformed into a controller file. In addition, It changed all the render functions to individual functions named after what they render such as index, show and guardian.
• Similar changes have been made for the Admin.GuardianView file, replacing render function calls with index and guardian functions.

[ruilopesm]

Don't forget to replace this.