[Todo item] Add entry creation timestamp column topg_stat_replication

Hello hackers,
 
I have worked on following todo list item.
 
  - Add entry creation timestamp column to pg_stat_replication
    http://archives.postgresql.org/pgsql-hackers/2011-08/msg00694.php
 
This item looks like simple because necessary data was already exist.
So, I wrote a prototype patch.
 
test example>
postgres=# select pid, reply_time from pg_stat_replication;
-[ RECORD 1 ]-----------------------------
pid        | 4817
reply_time | 2018-07-31 12:00:53.911198+09
-[ RECORD 2 ]-----------------------------
pid        | 4819
reply_time | 2018-07-31 12:00:53.911154+09
 
 
Several candidates exist for the field name.
    - reply_timestamp
    - info_gen_timestamp
    - stats_reset
    - last_msg_send_time
 
Feedback and suggestion will be very welcome.
Thanks!
 
Best regards,
Myungkyu, Lim