pgsql: doc: Clarify pgbench reporting with --continue-on-error

doc: Clarify pgbench reporting with --continue-on-error

Clarify that transactions failed under --continue-on-error are reported
separately and are not counted as transactions actually processed, while
time spent on them can lower reported TPS. Also adjust the latency
description to avoid implying that failed transactions are generally included
in latency measurements.

Backpatch to v19, where pgbench's --continue-on-error option was introduced.

Author: Chao Li <lic(at)highgo(dot)com>
Reviewed-by: Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>
Reviewed-by: Xuneng Zhou <xunengzhou(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/597C9755-4386-488D-A289-16D50AD81FBF@gmail.com
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ed23f7ce7f8f633175ae785d18577fbc440139ae

Modified Files
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doc/src/sgml/ref/pgbench.sgml | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)