Bug 32115: Add ID to check-out default help message dialog to allow customization

This adds a div with the id attribute selfcheckdefaulthelpmessage to
the first paragraph of the web based self check help page.

To test:
* Enable WebBasedSelfCheck
* Go to: /cgi-bin/koha/sco/sco-main.pl in the OPAC
* Log in and open help
* Verify by looking at the source code, that the first paragraph
  starting with "If this is your first time..." now has an id.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

koha-tmpl/opac-tmpl/bootstrap/en/modules/sco/help.tt

@@ -31,6 +31,7 @@
                         </div>
                     [% END %]
 
+                    <div id="selfcheckdefaulthelpmessage">
                         <p>If this is your first time using the self checkout system, or if the system
                         is not behaving as expected, you may want to refer to this guide to get
                         yourself started.</p>
@@ -50,6 +51,7 @@
 
                         <p>If you do not click the 'Finish' button, your session will automatically expire in
                         [% SelfCheckTimeout | html %] seconds.</p>
+                    </div>
 
                     <div class="button">
                         <a href="javascript:history.go(-1)">Return to the self-checkout</a>