fix: pricing table links to wrong page in docs (p2) (#7434)

## Summary

Continuation of updating pricing table link (p1 was
https://github.com/Comfy-Org/ComfyUI_frontend/pull/7402). Create a
constant since it's now used in multiple locations.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7434-fix-pricing-table-links-to-wrong-page-in-docs-p2-2c86d73d36508199b320d49faa6a0c73)
by [Unito](https://www.unito.io)

src/composables/useExternalLink.ts

@@ -92,8 +92,14 @@ export function useExternalLink() {
     comfyOrg: 'https://www.comfy.org/'
   }
 
+  /** Common doc paths for use with buildDocsUrl */
+  const docsPaths = {
+    partnerNodesPricing: '/tutorials/partner-nodes/pricing'
+  }
+
   return {
     buildDocsUrl,
-    staticUrls
+    staticUrls,
+    docsPaths
   }
 }