Alert types doc update

[arisonl]

There are a few issues with the opening paragraph of the 'Alert Types' document that we may want to address:

• Terminology for framework-level alerts: The term built-in alerts is used and it is likely that this term is a bit esoteric. In addition, in feature controls (subsequent release) we have named "built-in alerts" as stack alerts and we should probably stay consistent here.
• References to solution-specific alerts: We currently include links to solutions for the solution-specific types, but:
  • The links lead to generic pages, rather than the Observability alert pages, so the user needs to search through in order to discover the non-framework types. Even worse, it may cause some users to think that we only offer the alert types explicitly discussed in this page (i.e. the index threshold alert). Which leads to the next point:
  • The message should be clearer that more alert types are linked through this page. Particularly, because the page is titled "Alert Types" and it currently covers how to create an index threshold alert (in the absence of other framework-level alerts).

Let's also discuss if there is a viable way to keep all alert types in one place, although links are the best way to maintain always updated documentation. Also, let's make sure that any updates/changes we decide, propagate to other related pages accordingly.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)

[bmcconaghy]

@arisonl the docs have been updated to refer to these as "stack alerts" consistently. As for the other points, don't really see any way around this. We don't want to maintain docs for other alert types outside the docs for the apps that add them, so I think linking is the way to go. We need the maps team to add their own docs for the geo alert.