pgsql: Make GUC wal_sender_timeout user-settable

Make GUC wal_sender_timeout user-settable

Being able to use a value that can be changed on a connection basis is
useful with clusters distributed geographically, and makes failure
detection more flexible.  A note is added in the documentation about the
use of "options" in primary_conninfo, which can be hard to grasp for
newcomers with the need of two single quotes when listing a set of
parameters.

Author: Tsunakawa Takayuki
Reviewed-by: Masahiko Sawada, Michael Paquier
Discussion: https://postgr.es/m/0A3221C70F24FB45833433255569204D1FAAD3AE@G01JPEXMBYT05

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/db361db2fce7491303f49243f652c75c084f5a19

Modified Files
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doc/src/sgml/config.sgml            | 12 ++++++++----
doc/src/sgml/high-availability.sgml |  2 +-
src/backend/utils/misc/guc.c        |  2 +-
3 files changed, 10 insertions(+), 6 deletions(-)