Add callback before ticket metadata on update page

Add a callback that allows modify arguments before ticket metadata
or even skip the rendering of the original metadata section.

share/html/Ticket/Update.html

@@ -62,6 +62,10 @@
 
 <& /Elements/Crypt/SignEncryptWidget:ShowIssues, self => $gnupg_widget, Queue => $TicketObj->QueueObj &>
 
+% my $skip_metadata = 0;
+% $m->callback( CallbackName => 'BeforeMetadata', ARGSRef => \%ARGS, Ticket => $TicketObj, SkipMetadata => \$skip_metadata );
+% unless ($skip_metadata) {
+
 <div id="ticket-update-metadata">
   <&|/Widgets/TitleBox, title => loc('Ticket and Transaction'), class => 'ticket-info-basics' &>
 <div>
@@ -134,6 +138,7 @@
 
 % $m->callback( %ARGS, CallbackName => 'RightColumnBottom', Ticket => $TicketObj );
 </div>
+% }
 
 <div id="ticket-update-message">
 % if ( RT->Config->Get('SimplifiedRecipients', $session{'CurrentUser'}) ) {