Create separate config for Aspire project to fix PostgreSQL

> shouldn't this be taken from env variable in Aspire or we will have separate database named config files? AppHost.cs still has the `db-type` reference which can fail for PostgreSQL 

_Originally posted by @souvikghosh04 in [#3597](https://github.com/Azure/data-api-builder/pull/3597/changes#r3257615147)_

The Aspire project currently depends on the environment variable `db-type` for PostgreSQL. However, the default config we ship is `mssql`. Introduce a separate config that will fix usage of Aspire project for PostgreSQL.