feat: Tier 5 config screen — external DB toggle and generated password

[aa-replicated]

Summary

• Adds a database config group to kots-config.yaml with a db_type dropdown (embedded/external), a hidden auto-generated db_password_generated field (RandomString 32), and 5 conditional external DB connection fields (host, port, name, user, password) that appear only when external is selected
• Wires all new config values into helmchart.yaml: postgresql.enabled, postgresql.auth.password, and the full externalDatabase.* block

Rubric items addressed

• 5.0 — External stateful component toggle with conditional fields
• 5.2 — Generated default value (RandomString 32) that survives upgrade

Test plan

• Promote release in Vendor Portal after CI
• Install with embedded DB (default) — confirm gameshelf-postgresql-0 pod Running
• Upgrade — confirm app still connects without reconfiguration
• Install with external DB — confirm no postgresql pod, app connects to external instance

🤖 Generated with Claude Code