Added backed enum as possible role and permission name when finding or creating them

[EranNL]

When finding or creating roles and permissions, you can't use an enum like you can when assigning roles or permissions.
This PR adds support for backed enums when you find or create them.

Like so:

$permission = Permission::findOrCreate(PermissionEnum::VIEW_USERS);
$role = Role::findOrCreate(RoleEnum::ADMIN);