jobs: realm sync: fix scheduled LDAP syncs not applying attributes correctly

This was reported by a user in the forum [0].

The cause was that the user-* standard options were not registered
when the sync was called from the scheduler, resulting in the
following error:

  pvescheduler[2849]: skipping attribute mapping 'cn'->'comment' for user 'test@samba0' - no such standard option 'user-comment'

Fix this by simply importing the PVE::API2::User module, thus ensuring
the options get registered.

[0] https://forum.proxmox.com/threads/ldap-integration-comment-email-first-name-lastname.143490/

Fixes: cb93636 ("LDAP sync: improve validation of synced attributes")
Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
Reviewed-by: Fiona Ebner <f.ebner@proxmox.com>
Tested-by: Fiona Ebner <f.ebner@proxmox.com>

src/PVE/Jobs/RealmSync.pm

@@ -13,6 +13,9 @@ use PVE::Tools ();
 
 use PVE::API2::Domains ();
 
+# load user-* standard options
+use PVE::API2::User ();
+
 use base qw(PVE::Job::Registry);
 
 sub type {