[DOCS] Markdown insights/actions from investigation guide ("playbook actions")

[joepeeples]

Description

Related:

• https://github.com/elastic/security-team/issues/4824
• [Security Solution] Investigation guide - insights in markdown kibana#145240

Ongoing work to explore adding "playbook actions" to rule/alert investigation guides, similar to running Osquery from investigation guides (added in 8.5 - docs PR #2561).

Unclear what functionality, if any, will make it into 8.6.0 release, but we're creating this issue to monitor the feature as it's being finalized.