In order to view the primary segments' replication stream data from
their pg_stat_replication view, we currently need to connect to the
primary segment individually via utility mode. To make life easier, we
introduce a function that will fetch each primary segment's
replication stream data and wrap it with a view named
gp_stat_replication. It will now be possible to view all the cluster
replication information from the master in a regular psql session.

Authors: Taylor Vesely and Jimmy Yih