[RCA] Improve related alerts tab in the alert details apge

[maryam-saeidi]

Summary

In this PR, we added a new tab to the alert details page to show related alerts. This ticket is a follow-up to that work for implementing the following improvements:

1. Showing the number of active alerts in the tab
2. Selecting Rule name as the default group by and opening the first group
3. [Maybe] adding an event timeline to this tab (related to https://github.com/elastic/observability-dev/issues/3925)

[elasticmachine]

Pinging @elastic/obs-ux-management-team (Team:obs-ux-management)

[benakansara]

[Maybe] adding an event timeline to this tab (related to https://github.com/elastic/observability-dev/issues/3925)

I believe we have plan to include events timeline in alert details page #187112. @maciejforcone Can we show events timeline outside overview tab, so it's visible for all tabs?