Document index types in deployments docs

Description

Since 7.2, new indexes have be added by Liferay, workflow-metrics, liferay-search-tuning-rankings, and liferay-search-tuning-rankings and possibly others. These are called "app-driven" indexes.

App-driven indexes are not dropped and re-created upon a full reindex. In addition, app-driven indexex may not share the same index settings as the Virtual Instance (company) indexes.

Currently, there is no way to change the default index settings through the UI (System Settings). There is an open Feature Request for this on LPS-113030

Their settings aren't controlled in the same ways either - see LPS-114395.

The different indexes are described here: https://liferay.slack.com/archives/G982WB4TH/p1583272838022800?thread_ts=1583272838.022800

Company (aka. Virtual Instance) indexes (liferay-<companyId>
System index (liferay-0)
App-driven indexes
- OOTB (Workflow Metrics, Search Tuning - Result Rankings, Search Tuning - Synonyms)
- Custom app-driven indexes

Task:

Insure our documentation recognizes that only Company and System indexes are controlled by the settings described by LPS-114395.
Define the different types of indexes in the documentation
Document "workaround" for new deployments how to customize the index settings through the Override LPKG files mechanism, described here
On a separate article, we can provide information for developers how to create custom app-driven indexes