[Guided onboarding] [Security] Detect "Add data" step completion

[alisonelizabeth]

In 8.6, we will deliver the guided onboarding experience for Security.

The first step of the guided setup - "Add data" - involves adding the Elastic Defend integration and confirming incoming data. We will need a way to detect when the integration is added and relevant indices exist in order to mark this step as "complete" in the guided setup framework.

Implementation details

We should be able to check for the existence of the index logs.endpoint-events, but this needs to be confirmed. Alternatively, we can use the existing logic that detects that incoming data in the Integrations flow and mark the step completed from there.

[elasticmachine]

Pinging @elastic/platform-onboarding (Team:Journey/Onboarding)

[alisonelizabeth]

Addressed via #142185.