Slack integration drops segment create/update/delete events

[adamvialpando]

Summary

The Grafana integration posts annotations for segment create/update/delete events. The Slack integration sends nothing for the same events. Feature flag changes and segment overrides on a feature do reach Slack. We need to add standalone segment changes.

Steps to reproduce

1. Configure both the Grafana and Slack integrations on the same project, with the Slack config mapped to an environment.
2. Create, update, or delete a segment.
3. Compare the two integrations.

Observed: Grafana receives an annotation for the segment change. Slack receives nothing. A feature toggle and a segment override on a feature both post to Slack.

Expected: Segment create/update/delete events post to the configured Slack channel, matching Grafana.

Related issues (not duplicates)

• Slack integration doesn't notify on identity flag overrides (Edge / SaaS) #7983 Slack doesn't notify on identity flag overrides.
• Add link to audit log and relevant entities in Slack integration #4090 Add links to the audit log and entities in Slack messages.