feat: properly interpret forbidden error codes

[t-aleksander]

📖 Description

Core can return a forbidden error code during the enrollment. This change makes it so it's not converted into an internal server error.

🛠️ Dev Branch Merge Checklist:

Documentation

• If testing requires changes in the environment or deployment, please update the documentation (https://defguard.gitbook.io) first and attach the link to the documentation section in this pool request
• I have commented on my code, particularly in hard-to-understand areas

Testing

• I have prepared end-to-end tests for all new functionalities
• I have performed end-to-end tests manually and they work
• New and existing unit tests pass locally with my changes

Deployment

• If deployment is affected I have made corresponding/required changes to deployment (Docker, Kubernetes, one-line install)

🏚️ Main Branch Merge Checklist:

Testing

• I have merged my changes before to dev and the dev checklist is done
• I have tested all functionalities on the dev instance and they work

Documentation

• I have made corresponding changes to the user & admin documentation and added new features documentation with screenshots for users/admins