please add a 'postgresql-client' abstraction

Was setting up apache mod_apparmor for a site and needed the app to have access to a local postgresql database.

Looking for examples to copy, I found one commented-out example for rsyslogd of

  #/{,var/}run/postgresql/.s.PGSQL.*[0-9] rw,

(which, no, /var/run must die)

and another example on the Internet of

  /run/postgresql/** rw,

I wound up with

  /run/postgresql/.s.PGSQL.*[0-9] rw,

in my profile, but it would be good if this instead could be an abstraction.