pgsql: Suppress useless wakeups in walreceiver.

Suppress useless wakeups in walreceiver.

Instead of waking up 10 times per second to check for various timeout
conditions, keep track of when we next have periodic work to do.

Author: Thomas Munro <thomas.munro@gmail.com>
Author: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/CA%2BhUKGJGhX4r2LPUE3Oy9BX71Eum6PBcS8L3sJpScR9oKaTVaA%40mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/05a7be93558c614ab89c794cb1d301ea9ff33199

Modified Files
--------------
src/backend/replication/walreceiver.c | 171 ++++++++++++++++++++++------------
src/tools/pgindent/typedefs.list      |   1 +
2 files changed, 115 insertions(+), 57 deletions(-)