[IMP] website: add a default meta description on website pages

The goal of this commit is to add a default meta description on website
homepage and "contact us" page in order to improve their SEO and avoid a
warning of type `Document does not have a meta description`. Of course,
it is still meant to be overridden.

Part-of: odoo/odoo#140453

addons/website/data/website_data.xml

@@ -519,12 +519,14 @@
             <field name="url">/</field>
             <field name="view_id" ref="homepage"/>
             <field name="track">True</field>
+            <field name="website_meta_description">This is the homepage of the website</field>
         </record>
         <record id="contactus_page" model="website.page">
             <field name="url">/contactus</field>
             <field name="is_published">True</field>
             <field name="view_id" ref="contactus"/>
             <field name="track">True</field>
+            <field name="website_meta_description">This is the contact us page of the website</field>
         </record>
 
         <!-- Default Menu to store module menus for new website -->

addons/website/i18n/website.pot

@@ -11031,6 +11031,16 @@ msgid ""
 "additional content. This content is a little bit longer."
 msgstr ""
 
+#. module: website
+#: model:ir.ui.view,website_meta_description:website.contactus
+msgid "This is the contact us page of the website"
+msgstr ""
+
+#. module: website
+#: model:ir.ui.view,website_meta_description:website.homepage
+msgid "This is the homepage of the website"
+msgstr ""
+
 #. module: website
 #. odoo-python
 #: code:addons/website/controllers/form.py:0