Also add configuration file option "pgdata" for hard-coding the
node's data directory - if the "repmgr" DB user isn't a superuser
or doesn't have permission to extract the data directory, we'll
need another way of finding out.
This is needed for better switchover control, so we can instruct
the remote repmgr to issue the appropriate server command rather
than trying to work out what it should be from the local node.
This is only relevant when cloning a standby and the node's upstream
can change after failover/switchover etc., so no point keeping the
original value around in the configuration file.
This is more consistent with other parameters and conforms to
the pattern used by PostgreSQL itself, which uses the prefix "log_"
for logging parameters.
A warning will be emitted if the old version of the parameter name
is detected.
