feat: add optional PostgreSQL deployment support

[ibourgeois]

Context

As a developer deploying a Laravel app with Beacon, I need the option to deploy PostgreSQL alongside the application so I can stand up a usable environment with fewer manual steps.

Acceptance Criteria

• prompt the user to choose whether Beacon should deploy PostgreSQL
• generate Helm configuration for an optional PostgreSQL deployment path
• keep PostgreSQL deployment opt-in
• ensure the chart still works when PostgreSQL is disabled
• add tests for PostgreSQL-enabled and PostgreSQL-disabled chart output

Notes

PostgreSQL is the first database target for this workflow.