[IMP] base: add anchor to add action button in ir.model form view

In order to be able to add a button to activate contextual merge action on the
target model, the ir.model form view had to be adapted to add the header.

Task ID: 2459416
ENT PR: odoo/enterprise#16975

odoo/addons/base/views/ir_model_views.xml

@@ -31,6 +31,7 @@
             <field name="model">ir.model</field>
             <field name="arch" type="xml">
                 <form string="Model Description">
+                  <header><!-- used for override --></header>
                   <sheet>
                     <group>
                         <group>