feature/vsn-2706 - résolution du sub Keycloak pour les assignataires + synchronisation config auth

• Update keycloak/auth properties in config server (local/prerec/rec)
• Improve getSubForCollaborator() JavaDoc: clarify why Keycloak sub is stored vs UUID
• Add inline comments for better code readability

Fixes: assignees couldn't fetch tickets due to sub/UUID mismatch