[REF] website: convert default images to WebP format

This commit switches the default image format from JPEG to WebP for all
design-themes images. WebP offers superior compression compared to JPEG,
resulting in smaller file sizes and faster website loading times.
Additionally, this change helps avoid warnings from performance tools
regarding image optimization.

See also: odoo/odoo#168862

task-3167548

closes odoo/design-themes#805

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

theme_graphene/__manifest__.py

@@ -13,11 +13,11 @@
         'views/new_page_template.xml',
     ],
     'images': [
-        'static/description/graphene_poster.jpg',
-        'static/description/graphene_screenshot.jpg',
+        'static/description/graphene_poster.webp',
+        'static/description/graphene_screenshot.webp',
     ],
     'images_preview_theme': {
-        'website.s_cover_default_image': '/theme_graphene/static/src/img/pictures/bg_image_08.jpg',
+        'website.s_cover_default_image': '/theme_graphene/static/src/img/pictures/bg_image_08.webp',
     },
     'configurator_snippets': {
         'homepage': ['s_cover', 's_text_image', 's_numbers_grid', 's_mockup_image', 's_comparisons', 's_references'],