[FIX] theme_yes: fix s_call_to_action minor issues

This commit fixes three minors issues about the `s_call_to_action` snippet.

1) The `background-image` is missing the classes to set it to cover,
leading to a weird positioning of the image ;

2) The `background-image` was not the right one ;

3) The `s_call_to_action` snippet was missing from the theme screenshot.

task-4217986
follow-up of task-4178092

X-original-commit: 35ba43166a
Part-of: odoo/design-themes#971
Related: odoo/odoo#182039
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_yes/views/images.xml

@@ -206,7 +206,7 @@ Check in theme_kea's primary_variables.scss, theme.scss and theme_common's mixin
 <record id="s_parallax_default_image" model="theme.ir.attachment">
     <field name="key">website.s_parallax_default_image</field>
     <field name="name">website.s_parallax_default_image</field>
-    <field name="url">/theme_yes/static/src/img/snippets/s_parallax.jpg</field>
+    <field name="url">/theme_yes/static/src/img/snippets/s_parallax.webp</field>
 </record>
 <!-- // Company Team // -->
 <record id="s_company_team_image_1" model="theme.ir.attachment">

theme_yes/views/snippets/s_call_to_action.xml

@@ -3,7 +3,8 @@
 
 <template id="s_call_to_action" inherit_id="website.s_call_to_action">
     <xpath expr="//section" position="attributes">
-        <attribute name="style" add="background-image:url(/web/image/website.s_parallax_default_image)" separator=";"/>
+        <attribute name="style" add="background-image: url('/web/image/website.s_parallax_default_image');" separator=";"/>
+        <attribute name="class" add="oe_img_bg o_bg_img_center" separator=" "/>
     </xpath>
     <xpath expr="//div[hasclass('container')]" position="before">
         <div class="o_we_bg_filter bg-black-25"/>