Go & Postgres template docker-compose needs changing

[WWology]

Error: in 18+, these Docker images are configured to store database data in a format which is compatible with "pg_ctlcluster" (specifically, using major-version-specific directory names). 

This better reflects how PostgreSQL itself works, and how upgrades are to be performed. See also https://github.com/docker-library/postgres/pull/1259⁠ 

Counter to that, there appears to be PostgreSQL data in: /var/lib/postgresql/data (unused mount/volume) 

This is usually the result of upgrading the Docker image without upgrading the underlying database using "pg_upgrade" (which requires both versions). 

The suggested container configuration for 18+ is to place a single mount at /var/lib/postgresql which will then place PostgreSQL data in a subdirectory, allowing usage of "pg_upgrade --link" without mount point boundary issues. 

See https://github.com/docker-library/postgres/issues/37⁠ for a (long) discussion around this process, and suggestions for how to do so.

in the Go & Postgres template,

db:
  volumes:
    - postgres-data/var/lib/postgresql/data

causes error when postgres is using the latest image, this should be changed