Support of pgsql for postfix container

[monofox]

Summary

Currently, for lookups in extra.cfg for postfix within data/conf/postfix/ it is only possible to use either MySQL / MariaDB or local files with pcre, hash.

Feature request is to install the postfix-pgsql within the Dockerfile for Postfix in data/Dockerfiles/postfix/Dockerfile. With this, it is possible to add additional lookups from other containers using PostgreSQL without the need to build own container. E.g.:

virtual_alias_maps = proxy:mysql:/opt/postfix/conf/sql/mysql_virtual_alias_maps.cf,
  proxy:mysql:/opt/postfix/conf/sql/mysql_virtual_resource_maps.cf,
  proxy:mysql:/opt/postfix/conf/sql/mysql_virtual_spamalias_maps.cf,
  proxy:mysql:/opt/postfix/conf/sql/mysql_virtual_alias_domain_maps.cf,
  proxy:pgsql:/opt/postfix/conf/mailman/pgsql_virtual_alias_maps.cf

Motivation

Main advantage is, to make mailcow easily extendable for all users running partially other databases without need of keeping track to update or build own postfix container or whole project.

Additional context

postfix-mailcow_1    | May 12 19:32:25 2d6af700816b postfix/proxymap[387]: error: unsupported dictionary type: pgsql