Add cleanup_stuck_agent_platform_session event

What does this MR do and why?

This MR adds a cleanup_stuck_agent_platform_session event that is triggered when the FailStuckWorkflowsWorker cron drops the stuck sessions.

Changelog: changed EE: true

Relates to #557487 (closed)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Example:

1. Create a new workflow

curl POST --verbose \
    --header "Authorization: Bearer $GDK_TOKEN" \
    --header 'Content-Type: application/json' \
    --data '{
        "project_id": "flightjs/test-duo", "goal": "My goal", "agent_privileges": [1,2,5]
    }' \
    http://gdk.test:3000/api/v4/ai/duo_workflows/workflows

2. Make the workflow running stale

    w = ::Ai::DuoWorkflows::Workflow.last
    w.start
    w.update(updated_at: 4.days.ago)

3. Trigger CleanStuckWorkflowsService

::Ai::DuoWorkflows::CleanStuckWorkflowsService.new.execute

4. You should see the session status became failed

w.reload.human_status_name # should be failed

5. You should see a new analytics event at http://localhost:9093/micro/ui (see the gdk config get snowplow_micro.port for the correct port)

MR acceptance checklist

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