The pool_passwd option [1] is specified relative to config file. But for
greater flexibility absolute path should be accepted as well.
If pool_passwd option starts with /, let's treat it as absolute path.
Otherwise, it is treated as relative path.
Patch attached. Original author - Derek Kulinski [2]. In NixOS,
configuration files often end up in world readable store, which is not the
best place for storing password files.
[1]
http://www.pgpool.net/docs/latest/en/html/runtime-config-connection.html#GUC-POOL-PASSWD
[2] https://github.com/NixOS/nixpkgs/pull/66224