pgsql: doc: Explain when to use the WAIT NO_THROW option

doc: Explain when to use the WAIT NO_THROW option

The description of NO_THROW covered what the option does but not when an
application would want it. Explain that it suits callers that treat
timeout or not in recovery as expected results to be handled as part of
ordinary control flow, note the obligation to check the returned status,
and give the reason to omit the option.

Be precise about the option's scope: it changes only how those two wait
outcomes are reported. Soften the description's claim that the command
"returns a status string instead of throwing errors" accordingly, and say
that invalid input still raises an error, as does any condition checked
before the wait begins. Name two of those conditions as examples rather
than listing them, since the set grows.

Author: Rithvika Devisetti <devisettirithvika(at)gmail(dot)com>
Reported-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Reviewed-by: Kiran Kaki <itskkpg(at)gmail(dot)com>
Reviewed-by: Xuneng Zhou <xunengzhou(at)gmail(dot)com>
Reviewed-by: Satyanarayana Narlapuram <satyanarlapuram(at)gmail(dot)com>
Reviewed-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Discussion: https://postgr.es/m/14415b05-16d0-446f-ba7d-c891db8b3406%40eisentraut.org
Backpatch-through: 19

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e87c55f4d8b3fc3723e1f5d8ade7278e33bbb869

Modified Files
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doc/src/sgml/ref/wait.sgml | 37 +++++++++++++++++++++++++++++++++++--
1 file changed, 35 insertions(+), 2 deletions(-)