Schema API v2 Sample URLS refers to single node not solrcloud mode..

The v2 sample URLS on https://lucene.apache.org/solr/guide/8_1/schema-api.html reference modifying `/api/cores/

/schema`, but if you are in SolrCloud, you would send the request to `/api/collections/

/schema`.

We should reference the solrcloud mode in the sample docs, not standalone solr, as that is probably more common usecase for modifying schema.