pgsql: doc: Clarify passphrase command reloading on Windows

doc: Clarify passphrase command reloading on Windows

When running on Windows (or EXEC_BACKEND) the SSL configuration will
be reloaded on each backend start, so the passphrase command will be
reloaded along with it. This implies that passphrase command reload
must be enabled on Windows for connections to work at all. Document
this since it wasn't mentioned explicitly, and will there add markup
for parameter value to match the rest of the docs.

Backpatch to all supported versions.

Author: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Discussion: https://postgr.es/m/5F301096-921A-427D-8EC1-EBAEC2A35082@yesql.se
Backpatch-through: 14

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/9a26ff8c0e993e2fb3b3e48c3369996b7c2148dc

Modified Files
--------------
doc/src/sgml/config.sgml | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)