Fix postgres data folder for docker development

[maximusunc]

Developers have run into issues where the pgdata folder on their local machines don't have the correct permissions for postgres running in docker to fully manipulate, and that throws an error. A workaround is possible:

At the bottom of the compose.yml file, add:

volumes:
  pgdata:

and then under the shepherd_db service under volumes, change the line to:

- pgdata:/var/lib/postgresql/data

However, this workaround now moves all the postgres data inside of docker and the developer will have a harder time looking at the data.