feat: Add option to install and use postgres chart 8.x

If AUTO_DEVOPS_POSTGRES_CHANNEL is "2", we install the new 8.2.1 postgresql,
otherwise we use the old behaviour with respect to postgres

Also test auto_database_url in isolation

AUTO_DEVOPS_POSTGRES_CHANNEL uses increasing numbers, with 1 being the
oldest generation, and 2 being the newer generation.