[Stack Monitoring] Deprecate internal collection topics

We now have the ability to monitor Elasticsearch, Kibana, Logstash, Beats, and APM Server with Metricbeat. The previous method of monitoring stack products, using collection code internal to each product that shipped monitoring data to a custom Monitoring Bulk API endpoint, is now deprecated.

We should reflect this deprecation in documentation as well, specifically in these areas:

* [x] Stack docs: https://www.elastic.co/guide/en/elastic-stack-overview/current/xpack-monitoring.html
* [x] Elasticsearch: https://www.elastic.co/guide/en/elasticsearch/reference/current/monitor-elasticsearch-cluster.html
* [x] Kibana: https://www.elastic.co/guide/en/kibana/current/configuring-monitoring.html
* [ ] Beats: https://www.elastic.co/guide/en/beats/heartbeat/current/monitoring.html (Using Heartbeat as a sample here, but applicable to all Beats and APM Server documentation)
* [ ] Logstash: TBD; PR introducing Metricbeat collection is currently WIP: https://github.com/elastic/logstash/pull/11033

https://www.elastic.co/guide/en/beats/heartbeat/current/monitoring.html の未チェックの Beats monitoring ページから始め、チェック済みの Stack、Elasticsearch、Kibana のドキュメントリンクと比較します。内部の collection topics の非推奨化を反映するよう、該当する Beats および APM Server のドキュメントを更新します。参照されている PR が WIP でなくなったら、Logstash のドキュメントの場所を特定します。

索引モデルが issue の本文から書いたものです。