Yesterday, I was debugging a query in our application (with docker compose) and tried to enable some logs. A common pattern for this is to load a config file to some directory, that leaves default config intact but adds some parameters (I use Nginx and PHP containers, for example). So, I was very surprised that enabling some parameters is so hard to do with the Postgres image: it's required to maintain your own config fork, and then it's also required to change the default command?!

I did quick research, and learned, that Postgres also can include files of a directory as additional config. Therefore I created this PR to enable a similar experience in this container as well.

I implemented it in a similar way to what is already used to configure thelisten_addresses. With this change, it might not be needed to do it that way and we could as well just use a default configuration. I’m up for both, just let me know if I should implement it differently.

Basically, all this PR does is add the creation of the directory/etc/postgresql/conf.d and insert the lineinclude_dir = 'etc/postgresql/conf.d' into the default config.

With the suggested changes, it would be way easier to maintain and load one or even multiple config files, especially in local docker compose environments:
For example:

services:pg_configdir:image:postgresvolumes:     -db:/var/lib/postgresql/data     -${PWD}/config/postgresql/local/:/etc/postgresql/conf.dpg_configfiles:image:postgresvolumes:     -db:/var/lib/postgresql/data     -${PWD}/config/postgresql/local/default.conf:/etc/postgresql/conf.d/10-default.conf# - ${PWD}/config/postgresql/local/debug.conf:/etc/postgresql/conf.d/99-debug.conf   #optional: enable only for debugging