[ADD] web: ability to become superuser (uid=1)

* requires that current user has group_system
* only visible in debug mode (?debug)
* available at login or via debug menu
* special systray color in superuser sessions

Closes #27254

addons/web/static/src/xml/base.xml

@@ -247,6 +247,7 @@
     <div class="dropdown-divider o_debug_leave_section" role="separator"/>
     <a role="menuitem" href="#" data-action="split_assets" class="dropdown-item">Activate Assets Debugging</a>
     <a role="menuitem" href="#" data-action="regenerateAssets" class="dropdown-item">Regenerate Assets Bundles</a>
+    <a t-if="manager._is_admin" role="menuitem" href="/web/become" class="dropdown-item">Become Superuser</a>
     <a role="menuitem" href="#" data-action="leave_debug_mode" class="dropdown-item">Leave the Developer Tools</a>
 </t>
 <t t-name="WebClient.DebugManager.Action">