Implement PostgREST Auto-API Template

[NgocAnhDo26]

Background

Developers sometimes just need a fast RESTful API over a Postgres database without writing a backend. PostgREST does exactly this.

Specific Steps

• Create a template at apps/portal/examples/postgrest-template.
• Configure the HeliosApp CRD manifest to use the official postgrest/postgrest Docker image directly.
• Map Operator-injected DB_USER and DB_PASSWORD to PostgREST's required PGRST_DB_URI format (coordinate with Enhance Operator & CUE to Inject Formatted DB Connection Strings #60 @NgocAnhDo26 ).
• Create and test template.yaml.

Expected Output

A user can scaffold a PostgREST component on Backstage that immediately exposes a REST API connected to their provisioned Postgres database.