Add Slack notification documentation for workflows

[mintlify-development]

Summary

Documents the new Slack notification feature for workflows that shipped in mintlify/server#4021.

Changes:

• Added notify field to the frontmatter fields table with link to new Notifications section
• Added new "Notifications" section explaining how to configure Slack notifications for workflow completion/failure
• Added example workflow demonstrating auto-merge with team notifications

Feature summary: Workflows can now send Slack notifications when they complete or fail. Users can specify channels and users by name or ID, and notifications show the workflow status and whether the PR was auto-merged or needs review.

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Note

Low Risk
Documentation-only changes that describe a new configuration field and provide examples; no production logic is modified.

Overview
Adds documentation for workflow notifications by introducing a new notify frontmatter field and a dedicated Notifications section that explains configuring Slack recipients (channels/users by name or ID) and prerequisites.

Also adds a new example workflow demonstrating automerge: true paired with Slack notifications so teams are alerted on completion/failure with PR status context.

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