Create username fields for User schema

Feature Request Template

Title (semantic)

Format: feat(scope): short description Example: feat(auth): add otp expiration check

Description

This merge request implements a new feature.

Checklist

• The feature has been fully implemented.
• Tests for the new feature are included and passing.
• User documentation/guides have been updated (if applicable).
• Impact on existing functionality has been considered.

Related Issue(s)

Closes #86 (closed)