Create an offline snapshot for air-gapped installation docs

## Why?
We have a group of customers that need to view all air-gapped installation docs in a single location. Since these customers don't have access to public internet, we should provide them with an offline snapshot of these air-gapped install docs.

## Existing air-gapped installation docs and current owners
- Logstash (David K and Karen): [https://www.elastic.co/guide/en/logstash/8.5/plugins-filters-geoip.html#plugins-filters-geoip-manage_update](https://www.elastic.co/guide/en/logstash/8.5/plugins-filters-geoip.html#plugins-filters-geoip-manage_update)
- Logstash *maybe* (David K and Karen): [https://www.elastic.co/guide/en/logstash/current/offline-plugins.html](https://www.elastic.co/guide/en/logstash/current/offline-plugins.html)
- Fleet and Elastic Agent Guide (Karen): [https://www.elastic.co/guide/en/fleet/current/air-gapped.html](https://www.elastic.co/guide/en/fleet/current/air-gapped.html)
- Fleet and Elastic Agent (Karen): [https://www.elastic.co/guide/en/fleet/7.17/fleet-overview.html#package-registry-intro](https://www.elastic.co/guide/en/fleet/7.17/fleet-overview.html#package-registry-intro)
- Elastic Cloud on Kubernetes (Arianna): [https://www.elastic.co/guide/en/cloud-on-k8s/master/k8s-air-gapped.html](https://www.elastic.co/guide/en/cloud-on-k8s/master/k8s-air-gapped.html)
- ECE (Arianna): [https://www.elastic.co/guide/en/cloud-enterprise/3.5/ece-install-offline.html](https://www.elastic.co/guide/en/cloud-enterprise/3.5/ece-install-offline.html)

## Supporting docs
- [https://discuss.elastic.co/t/upgrading-elastic-agent-via-fleet-in-an-air-gapped-environment-failing/297413](https://discuss.elastic.co/t/upgrading-elastic-agent-via-fleet-in-an-air-gapped-environment-failing/297413)
- [https://github.com/wise2c-devops/install-elastic-cloud-on-k8s](https://github.com/wise2c-devops/install-elastic-cloud-on-k8s)
- [https://github.com/elastic/kibana/issues/74614](https://github.com/elastic/kibana/issues/74614)

## Discussion points
- External dependencies
- Offline doc ownership
- Breaking changes ownership
- Potential home: [Elastic Installation and Upgrade Guide](https://www.elastic.co/guide/en/elastic-stack/current/index.html)

一覧にある Logstash、Fleet と Elastic Agent、ECK、ECE の air-gapped インストールページと、関連する補足リンクを確認します。まず外部依存関係、所有者、breaking changes に対する責任の所在を整理し、次に提案されている Elastic Installation and Upgrade Guide の配置場所を評価します。顧客が関連するすべての air-gapped インストールドキュメントに、1つのオフラインスナップショットでアクセスできれば完了です。

索引モデルが issue の本文から書いたものです。