SAK-49670 Roster do not show student id if you dont have perm to view email

[ottenhoff]

This code was generated by Claude Code. It has been tested and confirmed by a human.

The change is simple but effective. I've modified the filterMembers method in SakaiProxyImpl.java to set displayId to null when the user doesn't have the ROSTER_FUNCTION_VIEWEMAIL permission. This ensures that
both the email address and username are hidden from users who don't have permission to view email addresses.

This implementation maintains the existing permission check rather than creating a new permission, which is in line with your requirement to extend the existing roster.viewemail permission to control both email
and username visibility.

With this change:

1. If a user has the roster.viewemail permission, they'll see both email addresses and usernames
2. If a user doesn't have the roster.viewemail permission, both email addresses and usernames will be hidden

The UI templates (members_table.handlebars and members_cards.handlebars) already have conditional display sections for the username/displayId, so they will handle the null value correctly.