BUG #14860: pg_read_all_stats and pg_stat_replication

The following bug has been logged on the website:

Bug reference: 14860
Logged by: Mahadevan R
Email address: mdevan(dot)r(at)gmail(dot)com
PostgreSQL version: 10.0
Operating system: any
Description:

User with pg_read_all_stats privilege is not able to read
some columns (listed below) from the pg_stat_replication
view. This is because these columns come from the function
pg_stat_get_wal_senders(), and this function returns non-null
values only for superuser.

To reproduce, set up streaming replication, and a user with
pg_read_all_stats privilege and "select * from
pg_stat_replication". The following columns will be null:

state
sent_lsn
write_lsn
flush_lsn
replay_lsn
sync_priority
sync_state