To use PostgreSQL/YesSQL persistence, a dev should be able to use an appropriate Docker container

As suggested in #846 - [we would like to add direct support for a PostgreSQL Docker container] which may be integrated with the Elsa Docker container. This means that it will be easier to set up an Elsa-with-YesSQL-and-PostgreSQL-persistence environment using Docker.

This issue is to make whatever changes to the docker compose file in order to accomplish that.

[we would like to add direct support for a PostgreSQL Docker container]: https://github.com/elsa-workflows/elsa-core/pull/846#issuecomment-815747233