Обсуждение: pgsql: Doc: improve description of dump/restore's --clean and --if-exis

Doc: improve description of dump/restore's --clean and --if-exists.

Try to make these option descriptions a little clearer for novices.
Per gripe from Attila Gulyás.

Discussion: https://postgr.es/m/169590536647.3727336.11070254203649648453@wrigleys.postgresql.org

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/83c05ed46a9c7c8d8ec375696dbc9b582a6de2c1

Modified Files
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doc/src/sgml/ref/pg_dump.sgml    | 17 ++++++++++-------
doc/src/sgml/ref/pg_dumpall.sgml | 17 +++++++++++------
doc/src/sgml/ref/pg_restore.sgml | 18 +++++++++++-------
3 files changed, 32 insertions(+), 20 deletions(-)