fix: Add missing authorization to Identity endpoints (#1170)

- ChangePasswordEndpoint: Add RequireAuthorization() for logged-in users
- GetUserProfileEndpoint: Add RequireAuthorization() for logged-in users
- AssignUserRolesEndpoint: Add RequirePermission(Users.ManageRoles)
- GetUserPermissionsEndpoint: Add RequirePermission(Users.View)
- Add Users.ManageRoles permission constant

These endpoints were previously accessible without proper authorization checks.

Co-authored-by: jarvis <jarvis@codewithmukesh.com>

Author: iammukeshm