Build: Add sitemap_urls to Typesense to fix some missing API pages

Follows-up 6cf42a4. Some pages aren't getting indexed because,
unlike api.jqueryui.com, on api.jqueryui.com there isn't a listing of
all pages. This means it relies on the category pages to discover them,
but these are excluded via `stop_urls` which means the categories
are never even opened, much less followed and/or indexed.

Fix this by feeding the sitemaps directly to ensure full discovery
of all posts and pages.

Ref jquery/infrastructure-puppet#66
Ref jquery/jquerymobile.com@6651b1b

docsearch.config.json

@@ -4,6 +4,10 @@
     { "url": "https://api.jqueryui.com", "selectors_key": "api", "page_rank": 20 },
     { "url": "https://jqueryui.com", "page_rank": 10 }
   ],
+  "sitemap_urls": [
+    "https://jqueryui.com/wp-sitemap.xml",
+    "https://api.jqueryui.com/wp-sitemap.xml"
+  ],
   "// stop_urls": [
     "// Exclude URLs containing '?' such as /themeroller/?..."
   ],