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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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3f8b8ddea08a110e9f44af2b2e52312fca901eac

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