Use a spotlight frontmatter property for category landing pages (#53443)

src/frame/lib/frontmatter.js

@@ -262,6 +262,22 @@ export const schema = {
     octicon: {
       type: 'string',
     },
+    spotlight: {
+      type: 'array',
+      minItems: 3,
+      maxItems: 3,
+      items: {
+        type: 'object',
+        properties: {
+          article: {
+            type: 'string',
+          },
+          image: {
+            type: 'string',
+          },
+        },
+      },
+    },
     // END category landing tags
   },
 }