[TASK] Add Postfix as a Helm subchart in Silver umbrella chart

[maneeshaxyz]

What needs to be done?

Summary

Add a Postfix Helm subchart under the Silver umbrella chart so SMTP can be deployed through the same Helm workflow as other services.

Background

first working setup:

1. Deploy Postfix via Helm.
2. Mount main.cf and master.cf from chart-managed ConfigMap.
3. Expose SMTP and submission ports.
4. Keep first bring-up minimal (standalone startup first, deeper dependency wiring later).

Relevant Files

• Chart.yaml
• values.yaml
• Chart.yaml
• values.yaml
• deployment.yaml
• service.yaml
• configmap-postfix.yaml
• main.cf
• master.cf

Scope

1. Register Postfix as a dependency in umbrella chart.
2. Set Postfix image and SMTP ports in subchart values.
3. Add ConfigMap template to embed main.cf and master.cf.
4. Ensure Service exposes ports 25 and 587.
5. Keep first version simple and deployable.