docs: redirect /search/sql to the SQL reference

Production serves its "Query with SQL" page at /search/sql, and the same
page at /search/sql/index; both URLs return that page on
docs.lancedb.com. Only the /index form was redirected to /sql, where that
guide now lives, so the canonical URL would have 404ed. It now redirects
to the same destination.

docs/web/docs.json

@@ -163,6 +163,10 @@
       "source": "/enterprise/deployment",
       "destination": "/enterprise/deployment/index"
     },
+    {
+      "source": "/search/sql",
+      "destination": "/sql"
+    },
     {
       "source": "/search/sql/index",
       "destination": "/sql"