docs: add activity logs to PostHog AI data access list

PostHog AI can now query activity logs to answer questions like
"who changed this flag?" or "what was modified last week?"

This feature requires the audit logs feature (Scale/Enterprise plans).

Related to PR #47104

Author: inkeep[bot]

contents/docs/posthog-ai/overview.mdx

@@ -75,6 +75,7 @@ While working with PostHog AI, you will certainly share some information with it
 - Actions and cohorts
 - Event and property definitions
 - Data warehouse schema
+- Activity logs (requires audit logs feature)
 
 Based on that context, PostHog AI comes up with queries, runs them, and summarizes the results. Those results can be as high-level as a single number, or as detailed as a list of users with all their properties.