docs: add resend integration guide (#10268)

* initial guide

* initial draft

* finished draft

* address feedback

* add meta image

www/apps/resources/generated/files-map.mjs

@@ -591,6 +591,10 @@ export const filesMap = [
     "filePath": "/www/apps/resources/app/examples/page.mdx",
     "pathname": "/examples"
   },
+  {
+    "filePath": "/www/apps/resources/app/integrations/guides/resend/page.mdx",
+    "pathname": "/integrations/guides/resend"
+  },
   {
     "filePath": "/www/apps/resources/app/integrations/guides/sanity/page.mdx",
     "pathname": "/integrations/guides/sanity"