add the source of param misconfigurations to error messages

Hi Hackers -

The command 

$ postgres --config-file="/etc/postgresql/10/main/postgresql.conf"

can fail with the following error:

postgres: superuser_reserved_connections must be less than max_connections

even if max_connections > superuser_reserved_connections in that config file

This is due to the addition of the postgresql.auto.conf params. 
Would the community welcome a patch whereby this detail in contained in the error? 

something to the effect of:

postgres: superuser_reserved_connections must be less than max_connections (superuser_reserved_connections is set to 10
in$path$ and max_connections is set to 10 in $path$)
 

Alternatively, we can track alter system changes in the postgresql.conf, so we have a unified source of parameter
configurations.

Thanks!


-- 
Jordan Deitch
https://id.rsa.pub/