Fetch the header (LCP) image at high priority (Shopify#1918)

sections/main-article.liquid

@@ -25,6 +25,7 @@
                 sizes="(min-width: {{ settings.page_width }}px) {{ settings.page_width | minus: 100 }}px, (min-width: 750px) calc(100vw - 10rem), 100vw"
                 src="{{ article.image | image_url: width: 1100 }}"
                 loading="eager"
+                fetchpriority="high"
                 width="{{ article.image.width }}"
                 height="{{ article.image.height }}"
                 alt="{{ article.image.alt | escape }}">