Make Postgres have a log prefix more like what pgFouine requires

We'll still need a conversion script, but it should be easy.

pgFouine requires a log prefix of '%t [%p]: [%l-1] '.  We instead use
'%m [%c]: [%l-1] ' which contains strictly more data.  Specifically,
"%m" is "%t" (time) but with milliseconds and "%c" is "%p" (pid) but
with the process start time.

(imported from commit a0bb583b563bdea0ca19b8b21677df0b9a18092a)

servers/puppet/files/postgresql/postgresql.conf

@@ -575,5 +575,5 @@ log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'
 log_rotation_age = 7d
 log_rotation_size = 100MB
 log_min_duration_statement = 500
-log_line_prefix = '%m %c/%p '
+log_line_prefix = '%m [%c]: [%l-1] '
 log_lock_waits = on