IEBH-476: Add smtp configuration for notification service

[vmoshynskyi]

• Add smtp configuration for notification service.

[Copilot]

Pull request overview

Adds Vault/ExternalSecret wiring and Helm values to supply SMTP credentials/config to the notification service, enabling authenticated SMTP usage in the dev cluster.

Changes:

• Document a new Vault KV path (secret/notification) holding smtp-password.
• Extend the notification app’s ExternalSecret to sync smtp-password into the in-cluster notification-credentials Secret.
• Update dev notification Helm values to use the new SMTP relay settings and source SMTP_PASS from the Secret.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
docs/vault-secrets.md	Documents the new Vault secret entry for notification SMTP password.
clusters/dev/apps/notification/values.yaml	Adjusts SMTP-related env vars and wires SMTP_PASS from notification-credentials.
clusters/dev/apps/notification/templates/external-secret.yaml	Syncs smtp-password from Vault (secret/data/notification) into the Kubernetes Secret.

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