Fixed guest user role mapping

[blicknix]

Description

Fixes the default role assignments for guest users with external user management.

Related Issue

• Fixes #665

Motivation and Context

This fixes the out of the box default roles for the deployment with oidc deployments.

How Has This Been Tested?

• Tested with keycloak and openldap externam idp

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Technical debt
• [ ] Tests only (no source changes)

Checklist: