feat: update site-wide Open Graph preview image to og-image.png

Author: khanhthanhdev

_config.yml

@@ -70,7 +70,7 @@ max_width: 930px
 # see https://schema.org/docs/faq.html for more information
 serve_og_meta: true # Include Open Graph meta tags in the HTML head
 serve_schema_org: true # Include Schema.org in the HTML head
-og_image: /assets/img/avt.webp # The site-wide (default for all links) Open Graph preview image
+og_image: /assets/img/og-image.png # The site-wide (default for all links) Open Graph preview image
 
 # -----------------------------------------------------------------------------
 # Analytics and search engine verification