[Feedback]: "Reindex documents" API documentation does not describe meaning of dest.routing parameter

### Was the documentation helpful?

No

### What documentation page is affected

https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-reindex#operation-reindex-body-application-json-dest-routing

### Description

The [Elasticsearch 8 API docs](https://www.elastic.co/guide/en/elasticsearch/reference/8.18/docs-reindex.html#docs-reindex-routing) included a nice description of how to use the `dest.routing` parameter to control routing:

> Reindex routing
>
> By default if `_reindex` sees a document with routing then the routing is preserved unless it’s changed by the script. You can set `routing` on the `dest` request to change this:
>
> `keep`
> Sets the routing on the bulk request sent for each match to the routing on the match. This is the default value.
> `discard`
> Sets the routing on the bulk request sent for each match to null.
> `=`
> Sets the routing on the bulk request sent for each match to all text after the =.

But the [new documentation page](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-reindex#operation-reindex-body-application-json-dest-routing) doesn't seem to describe at all what the parameter means or how to use it.