[IMP] website: add the possibility to add a header main button

Part of https://github.com/odoo/odoo/pull/49142
task-2229551

addons/website/views/snippets/snippets.xml

@@ -402,7 +402,7 @@
 
     <div data-js="menu_data"
          data-selector="#top_menu li > a"
-         data-exclude=".dropdown-toggle"
+         data-exclude=".dropdown-toggle, li.o_header_menu_button a"
          data-no-check="true"/>
 
     <div data-js="company_data"
@@ -502,6 +502,8 @@
                      data-customize-website-views="website.header_hoverable_dropdown"
                      data-select-class="o_hoverable_dropdown"
                      data-no-preview="true"/>
+
+        <we-checkbox string="Button" data-customize-website-views="website.header_button" data-reload="/"/>
     </div>
 
     <div data-js="TopMenuVisibility"

addons/website/views/website_templates.xml

@@ -315,6 +315,14 @@
     </xpath>
 </template>
 
+<template id="header_button" inherit_id="website.layout" name="Header Button" active="False">
+    <xpath expr="//ul[@id='top_menu']" position="inside">
+        <li class="nav-item align-self-md-center ml-1 o_header_menu_button">
+            <a href="/contactus" class="btn btn-primary">Contact us</a>
+        </li>
+    </xpath>
+</template>
+
 <!-- Features template -->
 <template id="login_layout" inherit_id="web.login_layout" name="Website Login Layout" priority="20">
     <xpath expr="t" position="replace">